OBJECTIVES This study sought to analyze the safety, efficacy, and follow-up results of percutaneous closure of secundum atrial septal defect (ASD) in young children. BACKGROUND Results of ASD transcatheter closure in adults are widely reported but there are no large published series concerning young children. METHODS Between December 1996 and February 2002, 48 of 553 patients percutaneously treated at our institution were children age less than or equal to5 years. Indications for closure were: elective closure in 32 patients; frequent respiratory infections in 8; failure to thrive in 2; liver transplantation in 5; and a fenestrated Fontan in 1. The procedure was carried out under general anesthesia with fluoroscopy and transesophageal control. Two different devices were used: 1) the CardioSEAL/StarFLEX (CS/SF) and 2) the Amplatzer septal occluder (ASO). Basal physical examinations and echocardiograms were performed prior to the procedure and at follow-ups (1, 6, and 12 months, and yearly thereafter). RESULTS The mean age at closure was 3.6 +/- 1.3 years. A CS/SF was used in 10 subjects; an ASO was used in 38 patients. No deaths or immediate major complications occurred. The total occlusion rate was 87% at procedure, rising to 94% at discharge. The mean follow-up was 18 +/- 14 months. No midterm major or minor complications occurred. The occlusion rate rose to 100% at 12 months of follow-up. Symptomatic patients improved significantly. CONCLUSIONS In the current era and in experienced hands, ASD closure can be performed safely and successfully, even in very young children. (C) 2003 by the American College of Cardiology Foundation.