Thirty-one autopsy cases of patients (20 men, 11 women) who died within 5 days of the onset of primary posterior wall myocardial infarction due to occlusion of the right coronary artery (RCA) were divided into two groups: Group A (19 cases) with associated right ventricular infarction and Group B 812 cases) without right ventricular extension of the infarct. The causes of death were practically identical in the two groups except for cardiac rupture which was always septal and more common in Group A. In Group A, the complete occlusion of the RCA was always proximal to (18 cases) or at the site of origin (1 case) of the right marginal artery. Twelve cases (63 p. 100) of tricuspid regurgitation were detected in Group A but there were no such cases in Group B. Tricuspid regurgitation was associated with a significantly poorer short term prognosis. It was not related to a greater degree of dilatation of the tricuspid ring but to more severe septal and right ventricular infarction causing prolapse of the septal and posterior septal leaflets into the right atrium. A second group of autopsy cases comprised 40 patients dying in the long term (1 to 14 years later) after primary posterior wall infarction. In 15 cases (Group A) the post-mortem study showed chronic right ventricular infarction, an extension of a chronic left ventricular infarct. These findings were absent in the other 25 cases (Group B). The mean survival times (Group A : 6.1 years, Group B : 5.9 years) were comparable.(ABSTRACT TRUNCATED AT 250 WORDS)