201Tl stress myocardial scintigraphy was performed in convalescent patients with acute myocardial infarction, to evaluate the influence of stenosis and collateral circulation of coronary artery in acute phase, on myocardial salvage in chronic phase. In 14 cases of unsuccessful coronary revascularization (complete occlusion), a complete defect of thallium imaging in chronic phase was seen in only one case of four cases with good collateral circulation, while eight of 10 cases with poor collateral circulation. In 16 cases of poor collateral circulation, six cases showed a complete defect, although the target vessel had improved to less than 75% of stenosis. However, in cases of good collateral circulation, no case showed a complete defect when the target vessel had improved to less than 75% of stenosis. The myocardial salvage is quite possible (p less than 0.05), when the coronary angiography in acute phase showed the forward flow (99% or 90% of stenosis) before coronary revascularization and/or good collateral circulation (Rentrop 2 degrees or 3 degrees).