The frequency and types of acute lesions in of 14 patients with unstable angina pectoris (UAP) not complicated by acute myocardial infarction were studied and compared to those in 32 patients with fatal acute myocardial infarction (AMI) and in 21 patients with sudden coronary death (SCD) in whom myocardial necrosis was absent. The frequency of intraluminal thrombi was significantly lower in the UAP group than in the AMI group (29% vs 69%, p=.02), and identical to that which was observed in the SCD group (29%). The frequency of plaque rupture was less in the UAP than in the AMI group (36% vs 75%, p=.02) and similar to that in the SCD group (36% vs 19%, p=0.4). Similarly the frequency of plaque hemorrhage in the UAP group was less than that in the AMI group (64% vs 90%, p=0.04) and not significantly different from that in the SCD group (64% vs 38%, p=0.2). Segments of artery containing multiluminal channels was greatest in the UAP group (12% in UAP vs 7% in AMI [P=.001] vs 7% in the SCD group [p=.004]). Thus, the types and frequency of acute coronary lesions were similar in patients with UAP and SCD.