In this study, factors leading to the failure of internal mammary artery grafting was investigated among patients with coronary bypass. In all, 1323 patients were evaluated. It was found that lower grade diameter stenosis in the native vessel during postoperative angiogram and wall motion score index independently affected the fate of internal mammary artery as a graft. Grafting with internal mammary artery to native vessels with lower grade stenosis and to myocardium with poor wall score might not be a rational approach.