This study aimed to assess the technical aspects of atrial septal defect (ASD) closure using the Amplatzer septal occluder (ASO) and the Gore Helex septal occluder (GHSO) for infants weighing less than 8 kg and to determine the safety, effectiveness, and near-to-intermediate-term outcome of the closure. The Mid-Atlantic Group of Interventional Cardiology Registry of percutaneous, transcatheter ASD closure procedures was reviewed for this analysis. Patients from 10 hospitals in the United States were included. The cohort for this report consisted of 68 patients weighing less than 8 kg (range, 2.3–7.8 kg; mean, 5.5 ± 1.6 kg) and ranging in age from 1 to 24 months (mean, 8.6 ± 4.7 months). The indications for ASD closure were failure to thrive, significant right heart enlargement, shunts otherwise thought to be hemodynamically significant, and poor overall clinical status. Devices were successfully implanted in 66 of the 68 infants (97.1 % procedural success rate). Five minor procedure-related complications occurred. At follow-up assessment, clinical status had improved significantly as measured by improved weight gain and decreased ventilator or oxygen dependence. All residual shunts spontaneously closed during the follow-up period. Six late deaths occurred, none of which were clearly device related. The ASO and GHSO can be safely and effectively implanted for ASD closure in infants weighing less than 8 kg. These procedures usually are successful and seldom complicated, resulting in significant clinical improvement.