Intracoronary streptokinase (STK) was given to 52 patients and 2 million U of intravenous urokinase was given to 15 patients with acute myocardial infarction less than 3 hr from onset of symptoms. Wall motion in the infarct region improved in 20 patients receiving STK alone (-2.5 +/- 1 to 2.1 +/- 1.1 SD/chord) and in 22 patients receiving STK and undergoing coronary bypass surgery within 24 hr (-2.5 +/- 1 to -1.5 +/- 1.0 SD/chord). Wall motion was unchanged in 10 patients not successfully reperfused with STK (-2.9 +/- 0.7 to -3.1 +/- 0.7 SD/chord). Regional wall motion improved at least 1.0 SD/chord in 71% of 14 patients treated within 2 hr of onset of symptoms, but in only 29% of 34 treated after 2 hr. Mean coronary artery stenosis after thrombolysis was 77 +/- 9%. Rethrombosis was associated with a stenotic cross-sectional area of less than 0.4 mm2. Ventricular function did not improve, with a residual stenosis of 0.4 mm or less in diameter. The Western Washington randomized trial reported a 1 year mortality of 2.5% in 80 successfully reperfused patients, but a mortality of 23% in 13 in whom reperfusion was partial and of 14.6% in 41 in whom reperfusion failed. The improved survival with successful reperfusion and improved ventricular performance with early and more complete reperfusion has stimulated interest in the need for angioplasty and coronary artery bypass grafting after thrombolytic therapy.