To prospectively assess the predictive value of left ventricular (LV) thrombus anatomy for defining the embolic risk after acute myocardial infarction (AMI), 2 comparable groups of patients with a first anterior AMI (group A, 97 thrombolysed patients; group B, 125 patients untreated with antithrombotic drugs [total 222]) underwent prospective serial echocardiography (follow-up 39 +/- 13 months) at different time periods. LV thrombi were detected in 26 patients in group A (27%) and in 71 in group B (57%; p <0.005). Embolism occurred in 12 patients (5.4%; 1 in group A [1%] vs 11% in group B [9%], p < 0.04). At multivariate analysis, thrombus morphologic changes were the most powerful predictor of embolism (p <0.001), followed by protruding shape (p <0.01) and mobility (p <0.02). In patients untreated with thrombolysis, a higher occurrence of thrombus morphologic changes (48% vs 8%, p <0.002) and protruding shape (69% vs 31%, p <0.002) were observed, whereas thrombus mobility was similar in the 2 groups (18% vs 8%, p = NS). Thrombus resolution occurred more frequently in thrombolysed patients (85% vs 56%, p <0.002). Thus, after anterior AMI, changes in LV thrombus anatomy frequently occur and appear the most powerful predictor of embolization. A minor prevalence of thrombus, a more favorable thrombus anatomy, and a higher resolution rate may contribute to reduce embolic risk after thrombolysis.