Forty patients were catheterized for closure of atrial septal defects with the Rashkind patent ductus arteriosus umbrella device, a modified Rashkind umbrella device, and the newly designed Lock Clamshell Occluder. Patients weighed 8 kg or more (a requirement for transvenous access with the 11F delivery sheath) and had defects suitable for closure based on two-dimensional echocardiography. The new device was at least 1.6 times the diameter of the atrial septal defect as determined by balloon sizing at catheterization. Patients were followed up by telephone, clinical examination, and echocardiography at 6 months. We attempted closure in 34 patients, with atrial septal defects ranging in diameter from 3 to 22 mm; device sizes ranged from 17 to 33 mm. Initial device position immediately after release was correct in all patients. A cerebral embolus occurred in one elderly patient before device placement--the patient died 1 week later. Two instances of early device embolization occurred, and devices were retrieved by catheter without complication. Follow-up of 31 patients discharged with devices in place, for a total of 31 patient-years, has yielded no umbrella-related complications. Adequate imaging studies in 19 patients 6.5 months after device placement revealed no atrial shunt in 12; residual flow through separate, previously unrecognized atrial septal defects occurred in two; and small residual leaks (less than 3 mm) around devices were present in five patients. This initial success indicates that double-umbrella closure of atrial septal defects will aid in the treatment of intracardiac defects.