Transcatheter coil embolization of the patent ductus arteriosus (PDA) has been frequently used in children, especially for small lesions. It was attempted in 3 adults using Cook detachable coils. For 2 of the patients, relatively old age and heart failure were the reasons for choosing coil embolization of the PDA. In the remaining patient, who had Wolff-Parkinson-White syndrome, coil embolization was performed after radiofrequency catheter ablation of Kent's bundle. Their respective minimal PDA diameters were 5.0 mm, 4.5 mm and 4.0 mm measured by transesophageal echocardiography. Two coils were placed in 2 patients and 1 coil in the remaining patient. After the procedures, the size of the left ventricle decreased and heart failure was improved in 2 patients, although all 3 patients had a residual shunt, which caused hemolytic anemia in 2 patients. Repeat coil-embolization procedures resulted in complete occlusion and the hemolysis disappeared in these patients. In adult patients who have heart failure due to large PDA, coil embolization with detachable coils, even if residual shunt persists, is useful for improvement of the heart failure. In cases of hemolysis related to residual shunt, a second coil-embolization procedure can improve it completely. (Jpn Circ J 1999; 63: 994 - 998)