The effect of early myocardial reperfusion (within six hours after the onset of symptoms) on left ventricular (LV) function in 106 patients with acute myocardial infarction was studied. The subjects consisting of 26 with conventional therapy, 19 with percutaneous transluminal coronary recanalization (PTCR), 16 with percutaneous transluminal coronary angioplasty (PTCA) after PTCR, 32 with direct-PTCA and 13 with coronary artery bypass graft (CABG) were randomly observed after 1981. In these patients, left ventricular ejection fraction (LVEF), regional wall motion, end-diastolic pressure and the contractility index were measured as the indices of LV function. 1. Compared to the conventional therapy group, LVEF and regional wall motion improved significantly in all groups with reperfusion therapy except in the PTCR group. This LV function in patients with subtotal obstruction or good initial collaterals significantly improved compared to patients with total obstruction and no collateral circulation. Patients with a 75 percent or more residual stenosis after reperfusion therapy had significantly decreased LV function compared to those with residual stenosis of less than 75 percent. These findings support the potential role for reperfusion therapy in patients with acute myocardial infarction.