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Abstract: Background: The impact of overload duration and age on remodelling process in human atria remains controversial. We analysed histological markers of right atrial (RA) remodelling in CHD patients in order to provide some insights into impacts of age and overload duration on substrates of atrial arrhythmias. Methods: Sixty-five CHD patients who underwent initial cardiac surgery were enrolled (median age 18years). Patients with dominant left atrial overload were excluded. RA tissues resected from CHD patients during surgery were examined by means of histology and immunohistochemistry and compared with RA tissues from age-matched control hearts from post-mortem (n=22, median age 22years). Patient histories of preoperative SVTs and echocardiography were also examined. Results: The greatest extent of fibrosis, the largest myocyte diameter and the longest capillary distance and the most CD45-positive cell infiltration was observed in CHD samples with SVT, followed by CHD without SVT and then control samples. All histological changes were correlated with age in CHD samples (r=0.462, 0.718, 0.529 and 0.447, respectively) with relatively steep and continuous manner, whereas only myocyte diameter was correlated with age in control samples (r=0.576). RA dimensions and area obtained from echocardiography also correlated with histological markers in CHD patients. Conclusions: Dominant and chronic RA overload due to CHD resulted in time-course related RA structural remodelling, which could provide the background for atrial arrhythmia. The overload duration, rather than age, seems to be a key factor for atrial histological degeneration in the cohort of CHD. [Copyright &y& Elsevier]