Among 100 consecutive autopsied cases of postinfarction rupture of the left ventricular free wall, 51% of the deaths were in-hospital and 49% were out of hospital. There were 51 men (mean age, 72 years) and 49 women (mean age, 76 years); 81% had multivessel disease. All had severe obstruction of at least one major epicardial coronary artery (98 atherosclerotic, one thrombotic, and one embolic). Acute coronary thrombosis was present in 73 cases and occurred on an atherosclerotic plaque in 72, 49 (68%) of which had associated plaque rupture. In 83 cases, the ruptured infarction represented the subject's first myocardial infarction. Despite a history of hypertension in 55 cases, appreciable left ventricular hypertrophy was observed in only 19 cases. By histopathologic age of infarction, 13 ruptures occurred during the first day, 45 between days 2 and 5, and 22 on days 6 and 7; thus, 58% occurred within 5 days and 80% within 7 days. The mid-ventricle was the most frequent site of rupture (66%). Ruptures most frequently involved the lateral aspect of the left ventricular free wall (44%). In 66 cases, the rupture tract occurred along the interface between viable and necrotic myocardium. Our findings support the observations of others that the risk factors for postinfarction left ventricular free wall rupture include age greater than 60 years, female gender, preexisting hypertension, absence of left ventricular hypertrophy, first myocardial infarction, and midventricular or lateral wall transmural infarctions.