The effect of selective intracoronary thrombolysis was studied in 27 patients with evolving myocardial infarction. In the acute phase, angiography demonstrated complete occlusion in 22 cases (81,5%) (group A), and incomplete stenosis with diminished distal blood flow in 5 cases (18,5%) (group B). Urokinase was infused into the infarct-related coronary artery at a rate of 8000 u/min u/min until reperfusion was obtained and subsequently at a rate of 2-4000 u/min for 20-40 min. In group A, coronary recanalization was achieved in 18 of 22 patients (81,8%) (group A1), while in 4 patients (group A2) the procedure was unsuccessful. Group B patients showed no angiographic modifications following fibrinolytic therapy. Left ventricular function was studied during the acute phase (before and after therapy) in 9 patients; 22 patients were studied immediately after thrombolysis and before hospital discharge. Preliminary studies of patients in group A1 after reperfusion showed a decrease in telediastolic pressure from 18,9 to 24,4 mmHg and an increase in ejection fraction from 0,40 to 0,43 (p = ns). No modifications in these parameters were observed in group A2 or B. Follow-up examination of group A, revealed an increase in ejection fraction from 0,40 +/- 0,12 to 0,50 +/- 0,15 (p less than 0,05) and a decrease in the length of the akinetic segment from 6,49 +/- 2,4 to 4,40 +/- 1,35 (p less than 0.05). In group B, the ejection fraction increased from 0,41 +/- 0,06 to 0,50 +/- 0,04 (p less than 0.05) and the length of the akinetic segment decreased from 7,52 +/- 2,0 to 3,38 +/- 1,14 (p less than 0.05). On the contrary, in group A2, ejection fraction diminished from 0,39 +/- 0,06 to 0,34 +/- 0,07 and the length of the akinetic segment remained unchanged. Our results suggest that: A) coronary artery thrombosis is frequent in evolving myocardial infarction B) selective intracoronary thrombolysis and subsequent reperfusion of the infarcted area is readily obtainable with urokinase infusion C) no significant acute modifications of left ventricular function were observed D) 2-3 weeks after initial treatment, patients in which recanalization of an occluded vessel was achieved (group A1) and patients that presented with subocclusive stenosis and reduced blood flow (group B), showed an improvement in left ventricular function and a reduction in the akinetic area.