A 73-year-old man underwent coronary-artery bypass grafting surgery on #4 PD and #7 with saphenous vein graft. Coronary arteriography and graft visualization performed on the 28th postoperative day revealed 75% concentric stenosis in the middle of the #4 PD graft. Before and after PTCA to the graft, examination by intravascular ultrasound imaging was performed and revealed that the stenosis was caused by fibrotic atheroma or thrombus. Intravascular ultrasound imaging appears to be useful in the field of cardiac surgery. It can be used in the follow-up of bypass grafts and also the detection of the entry site in dissecting aortic aneurysms. A brief review of the literature is given.