The relationship between estimated infarct size and cardiogenic shock was investigated in 317 consecutively admitted patients with acute myocardial infarction (AMI). Infarct size was estimated in vivo by serum CK-MB in all patients, and at heart autopsy by histological and histochemical techniques in 23 patients who died in hospital. Although patients with cardiogenic shock (n = 31) had a larger median serum CK-MB estimated infarct size than those without cardiogenic shock (1035 U/l v. 669 U/l, P less than 0.05) there was a substantial overlap in infarct size between the two groups. Heart autopsy confirmed this finding and demonstrated that patients with small subendocardial infarcts also died from shock, especially those with severe 2 or 3 vessel disease and/or infarction fibrosis. Those with cardiogenic shock who survived and those who died from shock had a similar median infarct size, and patients who died from other cardiac causes had the same median infarct size as those who died from shock.