We report our initial experience in three children with percutaneous transvenous closure of significant atrial septal defects. A newly developed one-piece nitinol device is delivered through a long venous sheath of 7 French calibre under fluoroscopic and transoesophageal echocardiographic monitoring. Complete closure of all defects was verified by echocardiography on the morning after the procedure. No complication occurred. In the first two patients, the device slipped sideways into the defect. This was easily discovered and corrected. Our experience shows that the Amplatzer® device is reliable, easy to implant, and presents very clearly on transoesophageal echocardiography and fluoroscopy. This makes implantation a controlled procedure. Until release, the device can easily be retracted into the sheath at any time and removed. The results suggest that closure of an atrial septal defect with this device is feasible, rapid, and safe.