The internal thoracic artery has been favored because of its superior early and late patency for coronary artery bypass grafting (CABG) in pediatric patients. We have studied the angiographic changes of the internal thoracic artery and its side branches before and after CABG with internal thoracic artery to the left anterior descending artery. The internal thoracic artery with remaining thymic or pericardial branches was patent but showed enlargement of the branches in the early period after the operation, and a postoperative exercise test suggested a remaining ischemic lesion in the bypass. Angiogram taken 1 year after CABG demonstrated the grown internal thoracic artery with disappearance of most of the side branches, which had been enlarged 1 month after the operation. Our findings suggest the importance of ligation of the whole proximal internal thoracic artery branches to maintain good early and late patency.