It is very important to evaluate the size of myocardial infarction and reversibility of ischemic myocardium in order to determine the severity and prognosis of patients with acute myocardial infarction. We performed thallium-201 redistribution myocardial scintigraphy and first pass radionuclide angiography in 12 patients with acute myocardial infarction. In eight cases, left ventricular wall motion was improved after nitroglycerin infusion (improved group), but in four cases it was unchanged (non-improved group). Six of the improved group showed a positive redistribution image, while in the non-improved group, no patient showed such an image. Ejection fraction increased after nitroglycerin infusion in the improved group, but unchanged in the non-improved group. There was no significant difference in hemodynamic parameters between the two groups at the time of admission, and after treatment hemodynamic parameters changed in the same way in both groups. In coronary angiography, three collateral channels were observed in the improved group, but none in the non-improved group. The severity of coronary artery stenosis in the two groups was almost identical. In eight patients, their regional ventricular wall motion improved after nitroglycerin administration, but there were four patients whose regional ventricular wall motion was unchanged. In both groups, hemodynamic and coronary angiographic findings were not different. But there were many positive redistribution images and collateral channels in the improved group. This result shows that reversible ischemia is indispensable for the improvement of regional wall motion. There was a case which showed a positive redistribution image on acute phase Tl-201 scintigraphy and a transient defect on the chronic phase exercise Tl-201 scintigraphy. But after the improvement of ischemia by aorto-coronary bypass operation, the defect on Tl-201 scintigraphy decreased and the wall motion improved. Neither redistribution on acute phase scintigraphy nor a transient defect on chronic phase exercise scintigraphy was observed in the non-improved group. From these data we conclude that the improvement of regional wall motion depends on reversible ischemia.