Device closure of oval fossa atrial septal defects with the Amplatzer Septal Occluder was performed in 26 patients ranging in age from 0.89 to 60.44 years. In eight additional patients no device implant was performed because of the presence of multiple defects or because the defect was of a size unsuitable for closure with the devices currently available. The stretched diameter of the defects that were closed ranged from 4 to 23 mm (mean 14+/-5.4 mm) and device sizes ranged from 4 to 24 mm. Two devices were unstable, of which one embolized to the right atrium after release. Both devices were retrieved at the same procedure. One of these patients subsequently underwent a successful device closure of his defect using a larger (24-mm) device. Three patients had multiple defects, which were successfully closed with a single device. At 1-month follow-up 23/26 (88%) and at 3-month follow-up 22/24 (92%) patients had complete closure of their defects, while two had residual shunts. One further patient who had complete closure of his defect at 1-month post-implant had his device removed and his atrial septal defect patched surgically 8 weeks after device closure. This was done as a result of the development of a vegetation affecting the device after an episode of septicaemia, which was not related to the cardiac problems. There was no procedure-related morbidity or mortality and all patients remain well at the present time.