BACKGROUND: Left ventricular thrombus is a common complication after acute myocardial infarction. Methods and RESULTS: To Study the incidence of left ventricular thrombosis (LVT) after acute myocardial infarction, we performed serial two-dimensional echocardiography (2D-Echo) in 35 consecutive patients with acute myocardial infarction prospectively ; 10 patients had inferior wall myocardial infarction, 25 patients had anterior wall myocardial infarction. 2D-Echo was obtained within 3 days of acute myocardial infarction, at 4-10 days after symptom onset, and 2-4 weeks after symptom onset serially in each case. 19 out of 35 patients received thrombolytic therapy with urokinase. Left ventricular thrombi were identified in 9(25.7%) of the 35 study patients. The location of myocardial infarction was anterior and apical in all cases with left ventricular thrombi. The shape of thrombi was mural in 6 cases and protruding in 3 cases. The incidence of left ventricular thrombi in patients who received urokinase was not significantly different from that in patients who didn't(31.9% vs 18.8%,p=0.22). Wall motion score was significantly higher in patients who developed left ventricular thrombi than in patients who had no left ventricular thrombus(8.2+/-1.9 vs 5.8+/-2.6, p<0.005). All thrombi appeared within 10 days after myocardial infarction. CONCLUSIONS: Thus left ventricular thrombi develops within 10 days following myocardial infarction with large anterior and apical location. The thrombolysis therapy has no effect in the incidence of left ventricular thrombi in this study. But because of confounding effect of thrombolysis and location of myocardial infarction and extent of myocardial infarction, further investigation is needed.