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Background Adult patients with congenital heart disease and a systemic right ventricle (sRV) are prone to develop heart failure. Decreased heart rate variability (HRV), a measure of autonomic dysfunction, is associated with morbidity and mortality in patients with congestive heart failure. The standard deviation of all intervals between normal sinus beats (SDNN) is a HRV parameter commonly reported as an indicator of autonomic function in these patients. Data about HRV and its clinical implications in patients with a sRV are scarce. Purpose To compare HRV parameters between patients with a sRV and healthy controls, and to assess their association with clinical status. Methods All available 24-hour Holter monitoring records of sRV patients under follow-up in our center and one record per healthy control subject were analysed. Holters with non-sinus rhythm were excluded. Time and frequency domain parameters were calculated and compared between both groups. Clinical landmarks such as arrhythmias or an episode of congestive heart failure, which occurred up until the time of the ambulatory ECG, were combined in a clinical event score. Determinants of SDNN were investigated with mixed model linear regression in the patients and with multivariate linear regression in the controls. Baseline characteristics, medication use, global longitudinal strain, validity as measured with bicycle exercise testing, and the clinical event score were taken into account. Results 113 Holters of 43 patients and 39 Holters of healthy controls were analysed. The patient group included 30 patients (70%) late after Mustard or Senning correction for transposition of the great arteries, and 13 patients with congenitally corrected transposition of the great arteries (30%). Age and gender were comparable in patients and controls. Several HRV parameters were significantly worse in patients compared with controls, including SDNN (138 in patients vs. 161 in controls, p=0.021). In the patients, clinical event score was the only significant determinant of a lower SDNN (p Conclusion Contrary to the healthy population, in patients with a sRV, HRV is associated with clinical status rather than age. This indicates that disease progression affects autonomic function more than ageing in this group. Further research is needed to clarify the relation between clinical outcome and autonomic function in sRV patients. Acknowledgement/Funding The Department of Cardiology of the LUMC received research grants from Medtronic, Biotronik, Boston Scientific and Edwards Lifesciences