The Amplatzer Septal Occluder (ASO) is the first and only device to receive full approval for clinical use in patients with secundum atrial septal defect (ASD) from the United States Food and Drug Administration. This study reports the device's initial results in Taichung Veterans General Hospital, a tertiary medical center in central Taiwan. Between October 2001 and December 2004, 39 consecutive patients (31 females, 8 males) with secundum ASD underwent attempt at transcatheter closure using the ASO under general anesthesia and transesophageal echocardiographic guidance. Six patients were excluded due to deficient rims (2 patients), multiple ASDs (1 patient), too large a defect (1 patient), too small a defect (1 patient) and 1 patient with associated atrial flutter. A total of 33 patients (26 females, 7 males) underwent the device closure procedure. The median age was 10.6 years (range 3.1-57.5 years) and median weight was 42 kg (range 13.5-73 kg). The median Qp/Qs ratio was 2.12 (range 1.02-5.52). The median balloon stretched diameter of the defect by sizing plate was 16 mm (range 5-37 mm). A total of 33 devices (median size 17 mm, range 7-38 mm) were implanted in 33 patients. The median fluoroscopy time was 10.1 minutes (range 5.9-29 minutes) and the median procedure time was 55 minutes (range 30-105 minutes). Complications included asymptomatic device embolization to the right ventricle in 1 patient (surgical removal) and transient complete atrioventricular block in 1 patient. Follow-up echocardiography at 10 minutes, 24 hours, 1 month, 6 months, 1 year and 2 years after the procedure showed complete closure rates of 76% (25/33), 91% (30/33), 100% (32/32), 100% (22/22), 100% (22/22), and 100% (9/9), respectively. In conclusion, transcatheter closure of secundum ASD using the Amplatzer Septal Occluder is safe and effective, with a very low complication rate.