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Coronary angiographic findings were compared in patients who presented with acute myocardial infarction (AMI, n = 75), unstable angina pectoris (UAP, n = 36), or stable angina pectoris (SAP, n = 36) for ≥2 years without evidence of any previous acute event and with an angiogram within 2 years of the initial symptoms. Angiograms were evaluated blindly for severity, extent (depending on the percentage of each coronary segment showing atherosclerosis), and pattern (discrete, <3 loci of narrowings involving <50% of any segment; diffuse, anything exceeding this). Patients in the SAP group had more narrowed arteries (2.4 ± 0.7 vs 1.3 ± 0.6 [p <0.021 and 1.4 ± 0.6 [p <0.021), more stenoses (6.0 ± 3.3 vs 2.1 ± 1.5 [p <0.01] and 2.6 ± 1.7 <0.05]) and occlusions (1.3 ± 1.1 vs 0.7 ± 0.6 [p = 0.05] and 0.3 ± 0.5 [p <0.02]), and a greater extent index (0.9 ± 0.5 vs 0.5 ± 0.3 [p <0.02] and 0.5 ± 0.3 [p <0.02]) than those in the AMI and UAP groups. Furthermore, a discrete pattern was less prevalent in patients with UAP than in those with SAP or AMI (3% vs 40% <0.02] and 25% [p <0.05], respectively). In conclusion, patients who present with acute coronary syndromes have less extensive atherosclerosis than those who present with chronic stable angina. Therefore, in the former group, coronary atherosclerosis appears to be more susceptible to ischemic stimuli responsible for acute coronary syndromes. Conversely, whether acute ischemic stimuli result in AMI or in UAP does not appear to depend on the severity of coronary atherosclerosis.