Transcatheter Gianturco coil embolization of 26 superfluous but hemodynamically significant vascular connections was attempted in 19 patients with congenital heart disease. There were 18 aortopulmonary collaterals, two vessels involved in pulmonary sequestration, two surgical aortopulmonary shunts (one inadvertently connected from the left subclavian artery to a left upper pulmonary vein), two cases of patent ductus arteriosus, one regurgitant left ventricular-to-descending aorta conduit, and a left superior vena cava-to-left atrium post Fontan procedure. The mean ratio of coil to vessel diameter was 1.6 +/- 0.7, and a mean of 1.5 +/- 1.1 coils were used per vessel. Occlusion was achieved in 24 of 26 attempts (92%), being complete in 21 (81%) and near complete (> 80% decrease in flow) in three (12%). Two attempts failed; a tortuous aortopulmonary collateral was engaged by the delivery catheter but the coil could not be advanced past an acute angle, and another aortopulmonary collateral had a narrow origin and enlarged distally, resulting in coil migration to a distal pulmonary artery branch. One patient had a transient decrease in leg pulses that resolved spontaneously. Fever occurred in four patients (21%) within 12 hours of coil placement, and resolved in all without sequelae or complications. A variety of undesirable vascular connections in patients with congenital heart disease can be safely and effectively treated by percutaneous coil embolization.