The effect of percutaneous transluminal coronary angioplasty (PTCA) upon regional myocardial perfusion (RMP) was studied in 49 patients (Group I) using T1-201 myocardial scintigraphy (TMS) after exercise. Ten patients with unsuccessful PTCA (Group II) were tested for the reproducibility of measurements and for comparison. All patients had arteriographically documented coronary artery stenosis (greater than or equal to 70%) in at least one major coronary vessel. In group I, average coronary stenosis was 84.0 +/- 7.8% (mean +/- SD) before PTCA and 38.8 +/- 11.9% after PTCA (p less than 0.001). TMS was performed 3 days before and 4 days after PTCA using an arm-assisted step test. Myocardial perfusion images were obtained 5-10 min, 1 hour and 3-4 hours following the injection of T1-201 in anterior, LAO 45 degrees and LAO 80 degrees views. The T1-201 myocardial scintigram was interpreted by the authors. Each scintigram (anterior, LAO 45 degrees and LAO 80 degrees) was divided into 5 roughly equal segments. The perfusion of each segment was graded from 0 (no perfusion) to 3 (normal perfusion). Thus, for each patient a "total myocardial perfusion index (TMPI)" could be calculated, with a score of 45 indicating normal RMP. The total number of involved segments (TNIS) was also calculated as a sum of abnormally perfused segments. In group II, the reproducibility of both TMPI and TNIS was satisfactory (r = 0.97 and r = 0.93, each p less than 0.001). In group I, TMPI before PTCA was 37.8 +/- 4.8 at 5-10 min, 39.8 +/- 4.4 at 1 hr and 40.8 +/- 4.2 at 3-4 hrs. These values increased significantly after PTCA to 41.3 +/- 4.0, 41.9 +/- 4.1 and 42.0 +/- 4.0, respectively (each p less than 0.001). TNIS also decreased significantly following PTCA. Group I patients were further divided into 2 groups: patients with and without previous myocardial infarction. Although patients with previous myocardial infarction had significantly lower TMPI values and greater TNIS values than without previous myocardial infarction, these parameters improved significantly after PTCA. Therefore, we conclude that PTCA can improve exercise induced regional myocardial ischemia, if luminal diameter is dilated by more than 20%. Patients with previous myocardial infarction and persisting angina are also considered to be candidates for PTCA.