The aim of this study was to compare left ventricular function, assessed by radionuclide angiocardiography, in 54 diabetics and 194 non-diabetics with acute myocardial infarction (AMI). The most meaningful results concern the inferior AMI group, whose left ventricular ejection fraction (LVEF) and regional wall motion were significantly lower in diabetics than in non-diabetics (LVEF was 44.2 +/- 11 vs. 51.6 +/- 9%, P less than 0.005; the regional wall motion score was 0.46 +/- 1 vs. 1.56 +/- 1, P less than 0.01, respectively), while no significant difference was observed in the anterior AMI group. However, in the group as a whole, the LVEF was 41 +/- 13% in diabetics and 47 +/- 13% in non-diabetics (P less than 0.01), the number of abnormally contracting segments was 2.0 +/- 0.9 and 1.5 +/- 1, respectively, and the wall motion score was 0.2 +/- 1.1 and 1.0 +/- 1.4, respectively (P less than 0.01). These data could be explained by an underlying cardiac dysfunction in diabetes, in addition to AMI. The more marked difference between diabetics and non-diabetics in inferior AMI might be related to the smaller infarct size in this group.