Five hundred and forty-eight patients who sustained their first acute myocardial infarction (AMI) were admitted to the coronary care unit (CCU). Ninety-eight of them were known diabetics. The diabetic patients were younger, 50 +/- 12 vs. 64 +/- 18 years of age (p less than 0.05), and the proportion of females in their group was higher than in the nondiabetics, 44% vs. 33.4% (p less than 0.05). The in hospital mortality rate was 30% for diabetics and 16% for nondiabetics (p less than 0.001). Diabetics had a higher percentage of mortality caused by left ventricular failure (LVF) (p less than 0.025) and a tendency for more frequent complete A-V block (p less than 0.01) compared to nondiabetics. Obesity and a positive family history for coronary heart disease were more prevalent in the diabetic group (both p less than 0.01). The echocardiographic assessment of left ventricular function, performed in 125 consecutively admitted patients (25 diabetics and 100 nondiabetics) on the 3rd-5th post-infarct day, showed that the indices of myocardial contractility, that is, E point septal separation (EPSS), ejection fraction (EF) and fractional shortening (FS) were far more impaired in diabetics than in nondiabetics (p less than 0.01, p less than 0.005, p less than 0.005, respectively). No significant difference was found in the prevalence of dyskinetic, akinetic and hypokinetic segments between the two categories of patients, suggesting no difference in the amount of myocardial mass affected by the AMI. Our results indicate that the increased incidence of LVF developed in diabetics after an AMI compared to nondiabetics may be caused by other factors, probably some form of latent diabetic cardiomyopathy as a result of either small vessel disease or metabolic disorder.