OBJECTIVE: Atrial septal defect (ASD) accounts for 6-10% of all congenital heart disorders. Secundum ASD closure can be performed surgically or percutaneously. We aimed to identify the various arrhythmias that occur before, during, and after the procedure and evaluate their management. METHODS: The study included a total of 427 patients aged 0-18 years who underwent transcatheter or surgical closure of isolated secundum ASD between January 2008 and January 2020. Postoperative electrocardiogram (ECG) traces, intraoperative arrhythmias, and treatments were recorded for both groups. Echocardiography and ECG were evaluated at postoperative 1 week, 1, 3, and 6 months, and annually thereafter. RESULTS: After transcatheter closure, follow-up basal ECG showed incomplete right bundle branch block pattern in 21 patients and sinus rhythm in 229 patients. After surgical closure, incomplete right bundle branch block pattern was detected in 23 patients, complete right bundle branch block in 3 patients, and complete AV-block (Atrioventricular Block) pattern in 1 patient. The other 150 patients showed sinus rhythm. At least one postoperative follow-up Holter ECG record could be obtained for 104 patients in the transcatheter group and 96 patients in the surgical group. Of 104 patients who underwent transcatheter closure, 97 (93.3%) had normal Holter ECG findings and 7 (6.7%) had arrhythmia. Of the 96 patients who underwent surgical closure, 85 (88.5%) had normal Holter ECG traces and 11 (11.5%) had arrhythmia. There was no statistically significant difference in the frequency of arrhythmia (P = 0.164). CONCLUSION: The higher frequency of arrhythmia in adult studies compared to the pediatric age group once again demonstrates the importance of early diagnosis and treatment of ASD in childhood. The similar incidence of arrhythmia in both groups supports the safety and effectiveness of both closure methods in eligible patients.