The late effects of thrombolytic therapy on regional left ventricular function and ventricular aneurysm formation were evaluated in 91 patients with acute myocardial infarction by two-dimensional echocardiography performed at 12 weeks and after one year follow-up. 53 patients were randomized to streptokinase plus heparin and 38 patients to heparin therapy alone. Wall motion score index (WMSI), asynergic area (AA) and left ventricular aneurysm were assessed in serial echocardiographic examination. During examination at 12 weeks of acute myocardial infarction significant differences between both groups of patients showed: WMSI 1.43 +/- 0.42 vs 1.78 +/- 0.61 (p < 0.005), AA 26.3 +/- 20.4 vs 39.4 +/- 22.8 (p < 0.01), left ventricular aneurysm 3(5.7%) vs 10(26.3%) (p < 0.05). After one year of examination significant differences persisted: WMSI 1.35 +/- 0.42 vs 1.62 +/- 0.59 (p < 0.05) AA 23.2 +/- 22.2 vs 35.8 +/- 24.8 (p < 0.02), left ventricular aneurysm 3(6.1%) vs 9(25.7%) (p < 0.05). Our data indicate that thrombolytic therapy improves late regional left ventricular function in patients with acute myocardial infarction by reducing the extent of regional wall motion abnormalities. We find evident reduction in aneurysm formation due to acute myocardial infarction in survivors after 12 weeks of observation. The mentioned beneficial effects are noted at least up to one year after acute myocardial infarction.