Objectives: Transcatheter closure of ASD has been accepted as a standard treatment for patient with hemodynamic significance in children and adults. Little is known about very small children and infants with poor weight gain and symptoms with congestive heart failure Methods: From April 2004 to March 2008, 316 patients underwent transcatheter closure of ASD using Amplatzer septal occludder (ASO, Golden Valley, MN) in our institute. Among them 24 patients were weighing 10kg or below (Device group). During same period surgical repair of ASD was performed in 134 patients and 16 patients were at the weight of 10kg or less (Surgery group). The indication of early treatment in each group was symptoms of congestive heart failure with volume overload of right side heart. We compared the demographic data, clinical characteristic and outcome of two groups. Results: In device group, there were 8 males and 16 females. Median age was 15months (7-15months) and average weight was 9.3kg (7.6kg to 10kg). Median ASD size was 15mm (10mm to 24mm). Two patients were sent to surgery because of the encroaching mitral valve by LA disk after device placement. The procedure was successful in rest of the patients. Surgery group consisted of 7 males and 9 females, median age was 12months (3-29months) and the mean size of ASD size was 15.9mm (10-24mm). There was no mortality in both groups. Complete closure rates at discharge were not significantly different (81.8% in device group and 87.5% in surgery group). In surgery group, there were 17 minor complications in 16 patients without major complication. In device group, only one minor complication was noted during the procedure (transient arrhythmia). The hospital stay was shorter in device group (4.7days) than in surgery group (15days). Conclusion: Transcatheter closure of secundum ASD with the ASO is technically feasible, safe and effective even in very small children and infants less than 10kg. The advantage of device closure over surgery appears similar in this small symptomatic patient group. Meticulous patient selection is of critical importance to avoid undue invasive procedures in this unique group of patients.