The prevalence of late reversibility in single photon emission computed tomography (SPECT) thallium 201 stress/redistribution studies is still controversial. The aim of our work was to evaluate the prevalence of late reversibility at infarct site in an unselected population of patients with previous acute myocardial infarction (AMI). We studied by SPECT thallium 201 and pharmacologic stress with dipyridamole (DIP) as well as by two-dimensional echocardiography 58 consecutive patients with previous AMI (50 men of mean age 57 years, range 40-73; 8 women of mean age 58 years, range 50-68). All the patients with perfusion defect at infarct site that was persistent at 4-hour study, were reimaged after 24 hours. Twenty-one (36%) of 58 patients complained about postinfarction angina. Following intravenous DIP (0.56 mg/kg), heart rate increased from 67 +/- 14 to 83 +/- 14 b/min (< 0.0001) and diastolic and systolic arterial pressures dropped from 86 +/- 12 and 139 +/- 25 mmHg to 79 +/- 14 and 132 +/- 27 mmHg, respectively (< 0.0001; < 0.0005). Of 57 patients with stress perfusion defects at infarct site, 16 (28%) demonstrated reversibility after 4 hours and 19 (33.4%) after 24 hours, with a total of 35 (61.4%) patients demonstrating reversibility by combined 4-hour and 24-hour imaging (< 0.0001 versus reversibility at 4-hour imaging alone). Thus, of 41 patients with 4-hour persistent thallium defects at infarct site, 19 (46.3%) demonstrated late reversibility.(ABSTRACT TRUNCATED AT 250 WORDS)