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Borderline left ventricle cases present considerable difficulties in determining the most effective surgical approaches. The evolution of approaches in the field has shifted from classical systemic pulmonary shunts to orthodox univentricular palliation and has subsequently seen the emergence of biventricular repair concepts. The concept of biventricular repair for borderline left heart conditions has developed through studies that aim to establish predictive scoring systems for identifying appropriate candidates. Despite continuous efforts, a definitive scoring system for guiding this decision is still difficult to find. There is a growing trend to provide neonatal patients with borderline ventricles with options other than univentricular palliation. Several centres have developed personalized strategies, including hybrid and staged ventricular recruitment approaches. These strategies provide sufficient time for personalized decision-making, taking into account the individual circumstances of each patient. This article presents an overview of the changing approaches to borderline left ventricular cases. It discusses the use of predictive scoring systems and emphasizes the advancements in staged strategies that improve the likelihood of successful biventricular repairs. [ABSTRACT FROM AUTHOR]

A heart with a borderline ventricle refers to a situation where there is uncertainty about whether the left or right underdeveloped ventricle can effectively support the systemic or pulmonary circulation with appropriate filling pressures and sufficient physiological reserve. Pediatric cardiologists often deal with congenital heart diseases (CHDs) associated with various degrees of hypoplasia of the left or right ventricles. To date, no specific guidelines exist, and surgical management may be extremely variable in different centers and sometimes even in the same center at different times. Thus, the choice between the single-ventricle or biventricular approach is always controversial. The aim of this review is to better define when "small is too small and large is large enough" in order to help clinicians make the decision that could potentially affect the patient's entire life. [ABSTRACT FROM AUTHOR]

Treatment options for hypoplastic borderline left ventricle (LV) are critically dependent on the development of the LV itself and include different types of univentricular palliation or biventricular repair performed at birth. Since hybrid palliation allows deferring major surgery to 4–6 months, in borderline cases, the decision can be postponed until the LV has expressed its growth potential. We aimed to evaluate anatomic modifications of borderline LV after hybrid palliation. We retrospectively reviewed data from 45 consecutive patients with hypoplastic LV who underwent hybrid palliation at birth between 2011 and 2015. Sixteen patients (mean weight 3.15 Kg) exhibited borderline LV and were considered for potential LV growth. After 5 months, five patients underwent univentricular palliation (Group 1), eight biventricular repairs (Group 2) and three died before surgery. Echocardiograms of Groups 1 and 2 were reviewed, comparing LV structures at birth and after 5 months. Although, at birth, all LV measurements were far below the normal limits, after 5 months, LV mass in Group 2 was almost normal, while in Group 1, no growth was evident. However, aortic root diameter and long axis ratio were significantly higher in Group 2 already at birth. Hybrid palliation can be positively considered as a "bridge-to-decision" for borderline LV. Echocardiography plays a key role in monitoring the growth of borderline LV. [ABSTRACT FROM AUTHOR]

Background Hybrid approach in hypoplastic left heart syndrome (HLHS) implies placement of bilateral pulmonary artery bands and ductal stenting. This approach serves as a less invasive surgical–interventional alternative to the Norwood procedure with reported equivalent survival. Potential benefits include deferrable surgical risks and in some borderline left ventricle patients, when combined with a restrictive inter-atrial communication, it offers a chance for biventricular circulation. Case summary Term newborn with total anomalous pulmonary venous connection (TAPVC), hypoplastic left heart, small aortic arch, and atrial septal defect (ASD) who was multi-disciplinary deemed eligible for a hybrid palliation performed on day six of life after TAPVC surgical correction. Subsequently, percutaneous ductal stent implantation was performed (two Sinus Superflex-DS stents) on day 11 of life. Magnetic resonance imaging (MRI) showed a hypoplastic non-apex-forming left ventricle (LV) [left ventricular end-diastolic volume index (LVEDVI) 15 mL/m2]. On day 27th of life, the ASD was closed surgically with a fenestrated patch. At 2 months of age, control cardiac MRI showed striking LV growth (LVEDVI 37 mL/m2). Herein an interventional hybrid take-down was performed with dilatation of both pulmonary arterial bands and closure of the ductal stent with an Amplatzer Vascular plug II, thus achieving biventricular circulation. Discussion Hybrid approach has proven as a safe alternative to the Norwood procedure for HLHS. This case illustrates the importance of multi-disciplinary care in high-risk two ventricular patients by means of LV rehabilitation. Further studies are needed to systematically define and understand the intricacies of potential candidates for staged biventricular repair initially managed with hybrid approach. [ABSTRACT FROM AUTHOR]

The aim of this review is to highlight the strengths and limitations of major echocardiographic biventricular repair (BVR) prediction models for borderline left ventricle (LV) in complex congenital heart disease (CHD). A systematic search in the National Library of Medicine for Medical Subject Headings and free text terms including echocardiography, CHD, and scores, was performed. The search was refined by adding keywords for critical aortic stenosis (AS), borderline LV, complex left ventricular outflow tract (LVOT) obstruction, hypoplastic left heart syndrome/complex (HLHS/HLHC), and unbalanced atrio-ventricular septal defects (uAVSD). Fifteen studies were selected for the final analysis. We outlined what echocardiographic scores for different types of complex CHD with diminutive LV are available. Scores for CHD with LVOT obstruction including critical AS, HLHS/HLHC, and aortic arch hypoplasia have been validated and implemented by several studies. Scores for uAVSD with right ventricle (RV) dominance have also been established and implemented, the first being the atrioventricular valve index (AVVI). In addition to AVII, both LV/RV inflow angle and LV inflow index have all been validated for the prediction of BVR. We conclude with a discussion of limitations in the development and validation of each of these scores, including retrospective design during score development, heterogeneity in echocardiographic parameters evaluated, variability in the definition of outcomes, differences in adopted surgical and Interventional strategies, and institutional differences. Furthermore, scores developed in the past two decades may have little clinical relevance now. In summary, we provide a review of echocardiographic scores for BVR in complex CHD with a diminutive LV that may serve as a guide for use in modern clinical practice. [ABSTRACT FROM AUTHOR]

A small atrial septal defect with right-to-left shunt is useful for off-loading a dysfunctional right ventricle postoperatively. However, an atrial septal defect with left-to-right shunt may not be as useful for a dysfunctional left ventricle. Experimental data are limited at present. Thus, we reconsider the related physiology to guide future approach., (© The Author(s) 2024. Published by Oxford University Press on behalf of the European Association for Cardio-Thoracic Surgery.)

Treatment options for hypoplastic borderline left ventricle (LV) are critically dependent on the development of the LV itself and include different types of univentricular palliation or biventricular repair performed at birth. Since hybrid palliation allows deferring major surgery to 4–6 months, in borderline cases, the decision can be postponed until the LV has expressed its growth potential. We aimed to evaluate anatomic modifications of borderline LV after hybrid palliation. We retrospectively reviewed data from 45 consecutive patients with hypoplastic LV who underwent hybrid palliation at birth between 2011 and 2015. Sixteen patients (mean weight 3.15 Kg) exhibited borderline LV and were considered for potential LV growth. After 5 months, five patients underwent univentricular palliation (Group 1), eight biventricular repairs (Group 2) and three died before surgery. Echocardiograms of Groups 1 and 2 were reviewed, comparing LV structures at birth and after 5 months. Although, at birth, all LV measurements were far below the normal limits, after 5 months, LV mass in Group 2 was almost normal, while in Group 1, no growth was evident. However, aortic root diameter and long axis ratio were significantly higher in Group 2 already at birth. Hybrid palliation can be positively considered as a “bridge-to-decision” for borderline LV. Echocardiography plays a key role in monitoring the growth of borderline LV.

Abstract Severe aortic stenosis can be accompanied by various degrees of left ventricular underdevelopment. The assessment whether a borderline‐sized left ventricle can or cannot support the systemic circulation is crucial. The decision‐making still remains challenging. We present a case that illustrates that the development of haemodynamic parameters can be difficult to estimate, even in the long term. The patient went from biventricular to univentricular circulation and back and could finally be palliated by heart transplantation. Modern technology including long‐term mechanical cardiac support as a bridge to candidacy and drug therapy for pulmonary hypertension were vital to successfully combat a previously lethal disease.

Severe aortic stenosis can be accompanied by various degrees of left ventricular underdevelopment. The assessment whether a borderline‐sized left ventricle can or cannot support the systemic circulation is crucial. The decision‐making still remains challenging. We present a case that illustrates that the development of haemodynamic parameters can be difficult to estimate, even in the long term. The patient went from biventricular to univentricular circulation and back and could finally be palliated by heart transplantation. Modern technology including long‐term mechanical cardiac support as a bridge to candidacy and drug therapy for pulmonary hypertension were vital to successfully combat a previously lethal disease. [ABSTRACT FROM AUTHOR]

Hypoplastic left heart complex with "borderline left ventricle" and intact ventricular septum is a clinical conundrum for the congenital heart surgeon. The choice between neonatal biventricular repair and single ventricle palliation can be challenging, and the current tools to aid in the decision-making process fail to account for the morbidity associated with intermediate and late diastolic dysfunction. Staged ventricular recruitment, consisting of valvular repair techniques, resection of endocardial fibroelastosis, atrial septal restriction, and augmentation of pulmonary blood flow, has been shown to improve left ventricular size and function culminating in eventual biventricular circulation. Despite staged ventricular recruitment, some patients cannot undergo biventricular conversion. Strategies to address these complex patients, including the "reverse" double switch, are the next frontier in biventricular repair. [ABSTRACT FROM AUTHOR]

The article focuses on the outcomes of patients undergoing biventricular repair (BVR) after an initial hybrid Norwood approach as asalvage procedure in extremely sick infants; or as the initial palliation in patients with uncertain feasibility of single-stage BVR due to severeleft ventricular outflow tract obstruction; or as part of a left ventricle (LV) recruitment strategy in patients with borderline LVs.

OBJECTIVES: Patients with severe left ventricular outflow tract obstruction often suffer from impaired left ventricular function, endocardial fibroelastosis and borderline-sized structures. The early Ross-Konno operation can offer complete repair due to outflow tract stenosis and enable the functional recovery and growth of small structures. METHODS: Between 2008 and March 2017, 44 early Ross-Konno procedures were performed at our centre. Thirty-five patients were neo- nates, and 9 were infants less than 3months of age. A retrospective single-centre investigation was carried out analysing early and late deaths, postoperative complications and reoperations during the follow-up period. Potential prognostic influence factors as previous fetal interven- tion, associated lesions as presence of a VSD or hypoplastic aortic arch or severe endocardial fibroelastosis were examined. RESULTS: The in-hospital mortality rate was 7% (3 of 44), and the late mortality rate was 2%. There were no deaths in the group with ven- tricular septal defects (9 cases), and there was 1 death in the group with critical aortic stenosis without arch repair (1 of 24; 4%). The most deaths occurred in patients with critical aortic stenosis and aortic arch repair (3 of 11; 27%) (P = 0.012). Fifteen patients with foetal interven- tion had a mid-term survival rate of 87%. Reoperations were necessary in 19 of 40 surviving patients during a mean follow-up period of 5.9 years. CONCLUSIONS: The early Ross-Konno procedure can enable biventricular repair even in borderline left ventricles with good long-term outcome. Thus far, there were no reoperations at the level of the autograft or the left ventricular outflow tract in our cohort. The highest operative risk was observed in patients with critical aortic stenosis and aortic arch hypoplasia. [ABSTRACT FROM AUTHOR]

Surgical management of patients with borderline left ventricular dimensions requires adequate patient selection. Therapeutic concepts have emerged to promote left ventricular growth and achieve adequate dimensions for staged biventricular repair. The hybrid approach thereby uses bilateral pulmonary artery banding and ductal stenting for initial palliation. A restrictive atrial septum is usually left unaddressed to ensure antegrade left ventricular filling. Final repair focuses on relief of obstructive left-sided lesions such as mitral valve stenosis, endocardial fibroelastosis, aortic valve stenosis, and aortic arch obstruction. The initial hybrid procedure is less traumatic than primary relief of left-sided obstructions. It remains to be determined if early or delayed relief of obstructive lesions improves the chances to grow left-sided structures. [ABSTRACT FROM AUTHOR]

In most newborns with left heart obstruction, the choice between a single-ventricle or biventricular management pathway is clear. However, in some neonates with a 'borderline' left ventricle, this decision is difficult. Existing criteria do not reliably identify neonates who will have a good long-term outlook after biventricular repair (BVR). The objective of this study was prospective assessment of the outcome after BVR for newborns in whom the left ventricle (LV) was considered 'borderline' by an expert group. This study was a prospective follow-up evaluation of neonates with obstructive left heart disease related to a 'borderline' LV who underwent biventricular management between January 2005 and April 2011. Of 154 neonates who required intervention for left heart obstruction, 13 (7.8 %) met the echocardiographic (echo) inclusion criteria. At the first and last echo, the z-scores were respectively −1.76 ± 1.37 and −0.66 ± 1.47 ( p = 0.013) for the mitral valve, −1.02 ± 1.57 and −0.23 ± 1.78 ( p = 0.056) for the aortic valve, and 13.77 ± 5.8 and 20.85 ± 8.9 ml/m ( p = 0.006) for the LV end-diastolic volume. At this writing, all 12 survivors are clinically well. However, LV diastolic dysfunction and pulmonary artery hypertension was present in 5 (36 %) of 12 patients. Endocardial fibroelastosis (EFE) was detected in five patients at the last follow-up echo, but only in two patients preoperatively. Cardiac magnetic resonance imaging did not confirm EFE in any of assessed patients. The study authors could not reliably predict the outcome after BVR for neonates with left heart obstruction and a 'borderline' LV. The presence of EFE with consequent diastolic dysfunction is more important than LV volume in determining the outcome. Prospective identification of EFE remains challenging. [ABSTRACT FROM AUTHOR]

Decision-making for biventricular repair (BVR) or univentricular palliation is challenging in neonates with hypoplastic left heart complex (HLHC). Hybrid strategy can be used successfully to achieve BVR in some of these patients. Between June 1998 and January 2022, 342 patients with a diagnosis of HLHS/variants, ductal-dependent lower body circulation with two ventricles, or HLHC with borderline left ventricle (LV) underwent initial bilateral pulmonary artery banding and ductal stenting in our institution. Among these 342 patients, 224 patients were defined as HLHS/variants and underwent univentricular palliation. 118 patients were determined to have borderline LV and hypoplastic left ventricular structures (HLHC, n = 48) or ductal-dependent lower body circulation with two ventricles (n = 70) considered suitable for BVR. 48 patients had multilevel obstructions including both aortic and mitral valve hypoplasia, aortic arch hypoplasia, and borderline LV. These were considered to have HLHC. These 48 HLHC patients are the subject of this report. Neonatal hybrid palliation at a median age of seven days was performed in 48 patients and 46 patients underwent BVR at a median age of 156 days. In 46 patients who underwent BVR, hospital mortality was not observed. The median follow-up was 66 months, with no late mortality. Heart transplant-free survival at 5, 10, and 15 years was 95.7%. 12 patients (26%) required reoperation and 9 (19.5%) required catheter reinterventions. Hybrid palliation may increase the chances for biventricular circulation in patients with borderline LV and small left-sided structures. Giessen hybrid approach as a left ventricular recruitment strategy achieves excellent early and long-term results.

In spite of great advances in staged left ventricle recruitment strategy, some patients do not achieve biventricular circulation nor are candidates for reversal to single-ventricle palliation. We present a case of a successful reverse double switch operation in a patient with failure of left ventricle recruitment and pulmonary hypertension. This strategy provided a one-and-a-half repair with a sub-pulmonary hypoplastic left ventricle that improved the patient's clinical status, becoming a novel alternative in this particular subset of patients., (© The Author(s) 2022. Published by Oxford University Press on behalf of the European Association for Cardio-Thoracic Surgery.)

Objectives: The goal of this study was to review results of a novel management strategy intended to rehabilitate the left heart (LH) in patients with LH hypoplasia who have undergone single-ventricle palliation (SVP). Background: Management of patients with hypoplastic LH syndrome and borderline left ventricle (LV) involves 2 options: SVP or biventricular repair. We hypothesized that staged LV recruitment and biventricular conversion may be achieved after SVP by using a strategy consisting of relief of inflow and outflow tract obstructions, resection of endocardial fibroelastosis, and promotion of flow through the LV. Methods: Patients with hypoplastic LH and borderline LV who underwent traditional SVP (n = 34) or staged LV recruitment (n = 34) between 1995 and 2010 were retrospectively analyzed and compared with a control SVP group. Results: Mean initial z-scores for LH structures before stage 1 SVP were not significantly different between groups. Mortality occurred in 4 of 34 patients after LV recruitment and in 7 of 34 after traditional SVP. LH dimension z-scores increased significantly over time after LV recruitment, whereas they declined after traditional SVP, with significant interaction between stage of palliation and treatment group. Restriction of the atrial septum (conducted in 19 of 34 patients) was the only predictor of increase in left ventricular end-diastolic volume (p < 0.001). Native biventricular circulation was achieved in 12 patients after staged LV recruitment; all of these patients had restriction at the atrial septum. Conclusions: In these patients with borderline LH disease who underwent SVP, it is possible to increase LH dimensions by using an LV recruitment strategy. In a subset of patients, this strategy allowed establishment of biventricular circulation. [Copyright &y& Elsevier]

The decision to perform biventricular repair for infants with multiple obstructive or hypoplastic left heart lesions (LHL) and borderline left ventricle (LV) may be controversial. This study sought to assess the mortality and morbidity of patients with LHL after biventricular repair and to determine the growth of the left-sided cardiac structures. Retrospective analysis of 39 consecutive infants with LHL who underwent biventricular repair was performed. The median age at surgery was 7 days (range 1-225 days), and the median follow-up period was 34 months (range 1-177 months). Between diagnosis and the end of the follow-up period, the size of the aortic annulus ( z-score −4.1 ± 2.8 vs. −0.1 ± 2.7) and the LV (LV end-diastolic diameter z-score −1.7 ± 2.8 vs. 0.21 ± 1.7) normalized. During the follow-up period, 23 patients required 39 reinterventions (62%) consisting of redo surgery for 21 patients (57%) and catheter-guided reinterventions for 8 patients (22%). At the end of the follow-up period, 25 of 34 patients were doing subjectively well; 10 children (29%) received cardiac medication; 12 (35%) presented with failure to thrive (weight ≤ P3) and 5 (15%) with pulmonary hypertension. The overall mortality rate was 13%. Biventricular repair for patients with multiple LHL results in sufficient growth of the left-sided cardiac structures. Nevertheless, residual or newly developing obstructive lesions and pulmonary hypertension are frequent, causing significant morbidity that requires reintervention. [ABSTRACT FROM AUTHOR]

We describe an infant with duct-dependent hypoplastic left heart complex with moderate hypoplasia of the left ventricle and aortic arch who was not operated due to resource limitations. The left-sided structures grew remarkably due to favourable loading condition changes of the left ventricle, allowing weaning from prostaglandin at the age of 3 months and discharging the patient without intervention.

Hypoplastic left heart complex with "borderline left ventricle" and intact ventricular septum is a clinical conundrum for the congenital heart surgeon. The choice between neonatal biventricular repair and single ventricle palliation can be challenging, and the current tools to aid in the decision-making process fail to account for the morbidity associated with intermediate and late diastolic dysfunction. Staged ventricular recruitment, consisting of valvular repair techniques, resection of endocardial fibroelastosis, atrial septal restriction, and augmentation of pulmonary blood flow, has been shown to improve left ventricular size and function culminating in eventual biventricular circulation. Despite staged ventricular recruitment, some patients cannot undergo biventricular conversion. Strategies to address these complex patients, including the "reverse" double switch, are the next frontier in biventricular repair., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Background: Single-stage biventricular repair remains a challenging and difficult decision in high-risk newborns and early infants with the presence of left ventricular outflow tract obstruction (LVOTO) or borderline hypoplasia of the left ventricle (LV)., Methods: Six high-risk patients underwent the initial hybrid procedure (bilateral pulmonary banding + ductal stenting) for staged biventricular repair. Their median age was 17 days (range: 7-55 days). The diagnosis was interrupted aortic arch (IAA), ventricular septal defect (VSD), and LVOTO (n = 3); IAA and VSD (n = 1); and aortic annular hypoplasia, aortic arch hypoplasia, VSD, and LVOTO (n = 1). The last patient had borderline LV with large atrial septal defect (ASD) and aortic arch hypoplasia. The patient with borderline LV had also ASD closure with small fenestration., Results: One patient died of sepsis after the hybrid procedure. Other patients underwent biventricular repair 8 to 13 months later. Three patients had conventional repair with conal septum resection. The other patient with IAA, in whom LVOTO was considered nonresectable, underwent Yasui operation. The last patient with borderline LV had enough development of left heart structures during follow-up and underwent aortic arch repair. One patient who had conal septum resection died after biventricular repair. One patient needed a tracheostomy; four patients were discharged uneventfully and their clinical conditions were good on postoperative year 1., Conclusion: Staged biventricular repair with the initial hybrid procedure may be a feasible and safe alternative in high-risk neonates and early infants. Hybrid intervention may provide the development of cardiac structures in time and a better evaluation for the possibility of biventricular repair in borderline patients.

Objective: Mitral valve anatomy has a significant impact on potential surgical options for patients with hypoplastic or borderline left ventricle. Papillary muscle morphology is a major component regarding this aspect. The purpose of this study was to use cardiac magnetic resonance to describe the differences in papillary muscle anatomy between normal, borderline, and hypoplastic left ventricles., Methods: We carried out a retrospective, observational cardiac magnetic resonance study of children (median age 5.36 years) with normal (n=30), borderline (n=22), or hypoplastic (n=13) left ventricles. Borderline and hypoplastic cases had undergone an initial hybrid procedure. Morphological features of the papillary muscles, location, and arrangement were analysed and compared across groups., Results: All normal ventricles had two papillary muscles with narrow pedicles; however, 18% of borderline and 46% of hypoplastic cases had a single papillary muscle, usually the inferomedial type. In addition, in borderline or hypoplastic ventricles, the supporting pedicle occasionally displayed a wide insertion along the ventricular wall. The length ratio of the superolateral support was significantly different between groups (normal: 0.46±0.08; borderline: 0.39±0.07; hypoplastic: 0.36±0.1; p=0.009). No significant difference, however, was found when analysing the inferomedial type (0.42±0.09; 0.38±0.07; 0.39±0.22, p=0.39). The angle subtended between supports was also similar among groups (113°±17°; 111°±51° and 114°±57°; p=0.99). A total of eight children with borderline left ventricle underwent biventricular repair. There were no significant differentiating features for papillary muscle morphology in this subgroup., Conclusions: The superolateral support can be shorter or absent in borderline or hypoplastic left ventricle cases. The papillary muscle pedicles in these patients often show a broad insertion. These changes have important implications on surgical options and should be described routinely.

Background: The term "borderline left ventricle" describes a small left heart that may be inadequate to provide systemic cardiac output and implies the potential need for a single-ventricle palliation. The aim of this study was to identify foetal echocardiographic features that help discriminate which infants will undergo single-ventricle palliation versus biventricular repair to aid in prenatal counselling., Methods: The foetal database at our institution was searched to identify all foetuses with borderline left ventricle, as determined subjectively by a foetal cardiologist, from 2000 to 2011. The foetal images were retrospectively analysed for morphologic and physiologic features to determine which best predicted the postnatal surgical choice., Results: Of 39 foetuses identified with borderline left ventricle, 15 were planned for a univentricular approach, and 24 were planned for a biventricular approach. There were significant differences between the two outcome groups in the Z-scores of the mitral valve annulus, left ventricular end-diastolic dimension, aortic valve annulus, and ascending aorta diameter (p<0.05). With respect to discriminating univentricular outcomes, cut-offs of mitral valve Z-score ⩽-1.9 and tricuspid:mitral valve ratio ⩾1.5 were extremely sensitive (100%), whereas a right:left ventricular end-diastolic dimension ratio ⩾2.1 provided the highest specificity (95.8%)., Conclusion: In foetuses with borderline left ventricle, a mitral valve Z-score ⩾-1.9 or a tricuspid:mitral valve ratio ⩽1.5 suggests a high probability of biventricular repair, whereas a right:left ventricular end-diastolic dimension ratio ⩾2.1 confers a likelihood of single-ventricle palliation.

“Hypoplastic left heart syndrome” is an unsatisfactory term describing lethal underdevelopment of the left ventricle (LV). It represents the more severe end of a spectrum of LV hypoplasia, mandating single-ventricle palliation or cardiac transplantation. Less severe “borderline” ventricular hypoplasia may instead allow various biventricular therapeutic strategies and better long-term outcomes. In this review, we consider factors causing and modifying the abnormal development of the LV. LV hypoplasia is typically seen in association with left ventricular outflow tract obstruction, itself part of a spectrum of related defects with common etiologies. Secondary responses to outflow obstruction are complex but involve abnormal flow dynamics and shear stresses that result in compromised and poorly orchestrated ventricular growth and development. Subsequent remodeling is likely influenced by genetic modifiers, including intrinsic myocardial growth signaling pathways, possibly including those of HAND transcription factors. In addition, during the latter stages of gestation, cardiomyocytes undergo a switch in myogenic potential and lose the ability to undergo mitosis. Ventricular hyperplasia can therefore no longer occur; remodeling is instead limited to muscular hypertrophy. Subtle differences in this switch in myogenic potential—and modulators thereof—are likely to be of clinical and therapeutic importance, especially in children with “borderline LVs” being considered for fetal interventions or post-natal biventricular repair strategies. Finally, by more clearly understanding the initiators and propagators of abnormal ventricular development, we can hope to lean away from grouping a heterogeneous group of infants together under the unsatisfactory term “hypoplastic left heart syndrome.” [ABSTRACT FROM AUTHOR]