In 22 patients with acute myocardial infarction, intracoronary infusion of streptokinase was begun 3.2 +/- 1.4 hours after the onset of symptoms. In 71% of patients recanalization of a completely occluded artery could be achieved. In 12 successfully treated patients left ventricular hemodynamics (left ventricular diastolic compliance and regional wall motion) were compared before and 4 weeks after recanalization. 4 weeks after intracoronary fibrinolysis left ventricular end-diastolic pressure had fallen (from 20 to 15 mm Hg, p less than 0.05), diastolic compliance had improved (p less than 0.05) and infarct size was reduced (p less than 0.05) compared to the acute stage of myocardial infarction. Left ventricular hemodynamics of 16 patients without heart disease (group A) and 22 patients with chronic myocardial infarction treated medically (group B) were compared to the findings of patients with acute myocardial infarction (group C). Group B and C showed reduced diastolic compliance as compared to group A (p less than 0.001). When group B and c were compared with identical size of akinesis (as measured by the number of asynergic hemiaxes), there was no significant difference of diastolic compliance. Reduction of diastolic compliance correlated linearly with infarct size (r = 0.73, r = 0.78). The results indicate that successful early reperfusion of acute myocardial infarction leads to a reduction of infarct size.