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 longterm outcome and incidence of arrhythmia following transcatheter device closure of secundum ASD. We evaluated cardiac dysrhythmias with ECG monitoring after transcatheter closure of ASD with Amplatzer device. A total of 155 consecutive patients with ASD underwent transcatheter closure of secundum ASD with Amplatzer device between October 2003 and December 2007. The study involved 35 of these patients assessed by 24-hour ambulatory ECG monitoring. Seven patients were evaluated a second time by 24-hour monitorization. baseline ECG revealed 85 patients had RBBB and 51 patients had RVH. 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 31 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 3.1 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.