BackgroundArrhythmia is one of the most common complications after cardiac surgery. The objectives of this study were to determine the prevalence and analyze the risk factors of postoperative arrhythmia in pediatric patients after cardiac surgery for congenital heart defects (CHD) at a single center in Bali, Indonesia over 2 years period.MethodsA cross‐sectional study, among 120 pediatric patients with CHD who underwent cardiac surgery, 92 patients met inclusion criteria in this study. The data were taken from medical records included demographic data, anthropometry, electrocardiography, surgical procedures, perioperative parameters, electrolyte levels, and management of postoperative arrhythmias.ResultsAmong 92 patients, 14 (15.2%) developed postoperative arrhythmias. Complete heart block (CHB) the most common arrhythmia, observed in five patients (35.7%), followed by supraventricular tachycardia three patients (21.4%). There were statistically significant differences between arrhythmia and nonarrhythmia groups for cardiopulmonary bypass (CPB) duration (171.23 vs. 108.01 min), aortic cross‐clamp duration (115.58 vs. 73.59 min), ischemia duration (106.33 vs. 65.43 min), and potassium level (3.33 vs. 3.88 mmol/L) with p < .05. Based on multivariate linear regression analysis, CPB time and potassium level were found to be independent risk factor.ConclusionsEarly postoperative arrhythmia observed 15.2% in this study, dominated by CHB. CPB duration, aortic cross‐clamping, ischemia time, and potassium level were statistically significantly different between arrhythmia and nonarrhythmia groups.