A 14-year-old boy, who had been treated medically for mitral regurgitation, underwent cardiac catheterization which revealed not only mitral regurgitation but also anomalous origin of the left coronary artery from the pulmonary artery. Thus he was diagnosed as Bland-White-Garland syndrome which was repaired by Hamilton's operation. Under cardiopulmonary bypass, the pulmonary trunk was opened longitudinally. After aorto-pulmonary window (A-P window) was created, a heterogenous pericardial baffle was attached to the posterior wall of the pulmonary trunk connecting A-P window and the ostium of left coronary artery. Thereafter the pulmonary trunk was enlarged with a patch of the same material. He did well postoperatively. Postoperative angiogram demonstrated satisfactory reconstruction of two-coronary-artery system.