To determine the relative frequency of the causes of death in the acute (less than 24 hours), early (24 hours to 3 weeks), and chronic (greater than 3 weeks) phases of myocardial infarction, data from all autopsies performed at a university hospital during a 56-month period were reviewed. Autopsies were performed in 56% of in-hospital deaths and 27% of patients dead on arrival in the emergency room (out-of-hospital deaths). In 271 cases of suspected cardiac death, a myocardial infarction of any age was identified. Death had occurred in the acute phase of a first infarction in 19 patients and was most frequently due to pump failure (37%) followed by cardiac rupture (26%) and arrhythmias (21%). Death had occurred 24 hours to 3 weeks after a first infarction in 80 patients and was most frequently due to pump failure (44%), rupture (27%), and arrhythmias (16%). Recurrent acute infarction was found in 32% of patients whose deaths were due to arrhythmias or pump failure and in 19% of those whose deaths were due to rupture. Death had occurred greater than 3 weeks after a first infarction in 172 patients. In 132 (77%) of these patients death was due to a complication of a new acute or recent infarction. Myocardial rupture was a less frequent cause of death in patients with recurrent infarction (8%) than in those dying in the acute or early phase after their first infarction (27%, p = 0.0009). A primary arrhythmia in the absence of recurrent infarction or ischemia accounted for only 14% of out-of-hospital deaths late after an infarction.(ABSTRACT TRUNCATED AT 250 WORDS)