Temporal changes in residual stenosis in the infarct-related coronary artery and ventricular function were studied in 30 consecutive patients with an acute myocardial infarction who received rapid, high dose intravenous infusions of steptokinase within 4 h of pain onset. Patients were studied 6 days and 3.9 ± 1.3 months after the acute episode. Inferior infarction, early thrombolysis (less than 1.5 h after pain onset) and adequate reperfusion (less than 75% residual stenosis in the infarct-related coronary artery) were associated with smaller left ventricular infarcts, smaller ventricular volumes and beter ventricular function. Residual stenosis tended to increase with time and in 6 patients the artery closed completely (1 with an overt clinical episode). Ventricular function and volumes improved progressively in patients with good initial function and less residual stenosis in the infarct-related coronary artery.