Transcatheter closure of atrial septal defect (ASD) has been used as an alternative to open heart surgery. Although transcatheter closure of ASD with the Amplatzer septal occluder is a safe and feasible method in pediatric patients, there is little published data on arrhythmia analysis following transcatheter device closure of secundum ASD. We evaluated cardiac dysrhythmias with 24-hour ambulatory electrocardiographic (ECG) monitoring after transcatheter closure of ASD with Amplatzer device. A total of 85 consecutive patients with ASD underwent transcatheter closure of secundum ASD with Amplatzer device between October 1998 and December 2003. The study involved 65 of these patients assessed by 24-hour ambulatory ECG monitoring. Seven patients were evaluated a second time by 24-hour monitorization. During the procedure, transient complete atrioventricular (AV) block was seen in two patients. One of them returned to normal sinus rhythm in catheterization lab and the other returned to normal sinus rhythm in two hours. Transient junctional rhythm was observed in another patient during the device placement. Twenty-four hour ambulatory ECG monitoring was performed on all patients after a mean four-month period (1-12 months). Holter recordings demonstrated rare supraventricular extrasystole in two patients, rare ventricular premature beats in two patients, and intermittent sinus arrest with sinus pause lasting <1.5 seconds in one patient, for a total of five patients (7.6%). In conclusion, dysrhythmias after transcatheter device closure of secundum ASD with Amplatzer device are rare and benign. We need further long-term follow-up to evaluate late dysrhythmias after the transcatheter device closure of secundum ASD.