Muscle viability in infarcted areas was evaluated based on the relationship between Tl myocardial scintigraphic findings and improvements in myocardial perfusion after percutaneous transluminal coronary angioplasty (PTCA) in 110 patients with old myocardial infarction (OMI). 1. Myocardial perfusion was improved in 95% of patients with redistribution in infarcted areas before PTCA, but in only 29% of patients without redistribution before PTCA. 2. The %Tl-uptake and the washout rate were significantly improved after PTCA in all patients with redistribution before PTCA with normal to dyskinesia of segmental wall motion. The %Tl-uptake of infarcted area after PTCA was greater than 50% in all patients. 3. The %Tl-uptake and the washout rate were significantly improved after PTCA in patients without redistribution before PTCA. However, the %Tl-uptake was not changed after PTCA in such patients with akinesia or dyskinesia of segmental wall motion. 4. Myocardial perfusion was improved late during prolonged follow-up after PTCA in 40% of patients without restenosis. Stunning of the myocardium is likely in these patients. 5. %Tl-uptake of more over 50% in patients with or without redistribution before PTCA indicates the presence of muscle viability. Muscle viability cannot be expected in the infarcted areas of patients without redistribution showing akinesia or dyskinesia of segmental wall motion. Patients without redistribution before PTCA include cases with underestimated ischemic lesion. The diagnosis of muscle viability by single photon emission computed tomography will be improved by including evaluation of segmental wall motion by echocardiography.