A 77-year-old female with two previous inferior myocardial infarctions was transferred to our medical center with a third inferior acute myocardial infarction. Coronary angiography revealed 99% stenosis with rich thrombus in the distal right coronary artery [Thrombolysis in Myocardial Infarction (TIMI) grade 2 flow]. The angiographic appearance of the right coronary artery was similar to the two previous myocardial infarctions. Coronary aspiration was performed and TIMI grade 3 flow was established. To confirm the presence of thrombus, intravascular ultrasound (IVUS) and coronary angioscopy were performed at pre-discharge. IVUS showed a thrombus-like low-density area at the mid right coronary artery. Red thrombi were observed in the same area using coronary angioscopy. Although warfarin had been prescribed for secondary prevention since the first acute myocardial infarction, both the second and third acute myocardial infarction occurred after cessation of warfarin. Patients with acute myocardial infarction due to thrombotic occlusion, confirmed by IVUS or angioscopy, might be good candidates for permanent warfarin therapy.