In 4,649 autopsies performed, in 1972-1985, 824 cases of acute myocardial infarction were found. Of these, 104 (12.6%) had cardiac rupture. Ten cases had rupture of the interventricular septum. The clinical and pathological records were reviewed, and the rupture group was compared with a control group of 100 patients who died from acute myocardial infarction without rupture. Of the patients with rupture, 85% died during the first week after the onset of myocardial infarction; three patients with rupture died suddenly without previous clinical evidence of myocardial infarction. Rupture occurred only in hearts with transmural infarcts, and predominantly in the anteroseptal wall. Patients with rupture had significantly higher blood pressure, fewer previous infarcts, higher frequency of coronary thrombi, less myocardial scar tissue and lower heart weight compared to the control group. There were no significant differences regarding age and sex distribution, physical effort at the symptom debut or death, medication, previous and present diseases other than infarcts, complications or the degree of atherosclerosis in the coronary arteries or aorta.