The purpose of this research was to analyze myocardial perfusion in patients with previous myocardial infarction (MI). The study was carried-out in 46 patients with symptomatic myocardial ischemia. Nineteen patients had a previous anteroseptal MI - 12 transmural and 7 non transmural; 5 lateral MI - 2 transmural and 3 non transmural; 22 inferior MI - 11 transmural and 11 non transmural. Six patients had critical stenosis of 1, 19 of 2, 21 of 3 coronary vessels; the patients with non transmural MI had a higher patency rate of infarcted-related vessels, as compared to the patients with transmural MI. In each patient, 2 mCi of thallium-201 were injected 60 s before the end of a symptom-limited bicycle exercise; images were taken 5 min after the exercise and 4 hours later, at rest. An irreversible perfusion defect was observed in 24/25 patients with transmural MI and in a smaller number (8/21) of patients with non transmural MI (p less than 0.001). A complete or partially reversible perfusion defect in the peri-infarction areas was observed in 9/25 patients with transmural MI and in 16/21 patients with non transmural MI (p less than 0.01). Reversible (12 patients) and irreversible (5 patients) perfusion defects were observed in myocardial segments different from those of MI. The planar qualitative thallium-201 scintigraphy presented a high sensitivity concerning the individuation of irreversible myocardial perfusion defects, localized in areas of a previous transmural MI. Thallium-201 scintigraphy was not a good predictor of the site of a previous non transmural MI.(ABSTRACT TRUNCATED AT 250 WORDS)