Twenty-five patients with acute myocardial infarction were examined for ventricular thrombi using two-dimensional echocardiography. Six of 10 patients (60%) with an anterior wall infarction had an apical or apical-septal thrombus within the first week of hospitalization. None of the fifteen patients with an inferior wall myocardial infarction had a mural thrombus. Although the size of infarction in the patients with a thrombus was not significantly larger than in those who had an anterior wall infarction without a thrombus (43% +/- 10% vs. 31% +/- 7%, P less than 0.1), the severity and extent of dyskinesia or akinesia were more marked in the former group. Left ventricular function as determined by the nuclear blood pool scan ejection fraction was also significantly less for the former group than for the latter group (21% +/- 6% vs. 40% +/- 11%, P less than 0.02). Three of six patients with an intracavitary thrombus on echocardiography had systemic embolic during their hospital course. Postinfarction ventricular thrombi tend to occur in those patients with an anterior wall myocardial infarction who have far advanced wall motion abnormalities of the affected area, and overall poor left ventricular function. Although the number of patients was small, the high incidence of systemic embolization in the infarction subjects with echocardiographically proven thrombi indicates that these patients are at increased risk for such events.