It has been shown that streptokinase administration at the time of acute myocardial infarction reduces mortality significantly, and that this reduction in mortality should be related to salvage of jeopardized myocardium and preservation of left ventricular function. To better define the relation between thrombolytic therapy and left ventricular modeling and function after acute myocardial infarction, 331 consecutive patients enrolled in the Gruppo Italiano per lo Studio della Streptochinasi nell'Infarto Miocardico trial were studied by two-dimensional echocardiography just before discharge from the hospital. A 6 month follow-up examination was also available in 232 of these patients. Ventricular volumes were computed from an apical four chamber view, according to a previously published algorithm. An infarct size index was also semiquantitatively assessed, according to the number of akinetic and dyskinetic segments in an 11 segment left ventricular model. At predischarge examination, the 161 patients assigned to streptokinase treatment showed smaller ventricular volumes (end-diastolic volume 119.3 +/- 49.7 versus 134.5 +/- 57.8 ml [p = 0.011]; end-systolic volume 65.4 +/- 36.4 versus 74.9 +/- 45.7 ml [p = 0.036]) and smaller regional wall motion index (2.2 +/- 1.9 versus 2.7 +/- 1.9 segments; p = 0.019) compared with values in the 170 patients assigned to standard care; there was no difference in ejection fraction (46.6 +/- 14.1 versus 45.9 +/- 14.9%; p = 0.64). For both groups of patients, there was a significant relation between end-systolic volume and regional wall motion index (p less than 0.001); for large and similar extents of infarct size, ventricular volume was smaller in patients assigned to thrombolytic treatment than in patients assigned to standard care. At 6 months' follow-up, the differences in volume and regional dysfunction detected at the early examination persisted: 110.8 +/- 47.6 versus 127.9 +/- 53.8 ml for end-diastolic volume (p = 0.001), 56.3 +/- 33.6 versus 69.4 +/- 42.1 ml for end-systolic volume (p = 0.001) and 1.8 +/- 1.8 versus 2.3 +/- 1.8 segments for regional wall motion index (p = 0.001). Again, for comparable extents of infarct size, end-systolic volume was smaller in patients who received streptokinase (n = 110) than in those assigned to conventional treatment (n = 122). It is concluded that streptokinase improves left ventricular modeling and function in patients with myocardial infarction, reducing the extent of regional wall motion abnormalities and lessening postinfarction ventricular dilation. The beneficial effects persist up to 6 months.