Quantitative evaluation of exercise T1-201 myocardial scintigraphy was carried out to determine the effect of transluminal coronary angioplasty (TCA) in 15 patients with critical coronary artery stenoses (greater than or equal to 70%). Thirteen lesions were successfully dilated (reduction in stenosis by more than 30%); two were unsuccessful. Calculated indices from T1-201 myocardial scintigraphy, using a semi-automatic computer image processing system, included washout factor (WF), vitality index (VI) and redistribution factor (RDF). No changes were noted in WF before and after dilatation. The VI increased in successfully dilated patients from 66.3 +/- 8.5% (mean +/- SD) to 77.8 +/- 10.9% (p less than 0.001) in the areas perfused by the vessels containing the lesions. The RDF decreased significantly after dilatation from 4.4 +/- 6.1% to 1.2 +/- 2.8% (p less than 0.05) 1 hour after exercise and from 10.4 +/- 7.5% to 4.1 +/- 4.2% (p less than 0.01) 3-4 hours after exercise. From these results, we conclude that the perfusion of ischemic areas distal to critical coronary artery stenoses improves following successful dilatation. T1-201 myocardial scintigraphy was shown to be very useful in the evaluation of TCA.