Tc-99m MIBI SPECT was used to assess the early benefits of successful percutaneous transluminal coronary angioplasty (PTCA) in nine consecutive patients. SPECT stress studies were done by artificial cardiac pacing just prior to PTCA and 16-20 hours later, with perfusion images obtained 2-3 hours after pacing stress and Tc-99m MIBI injection. Angiographic restenosis was demonstrated in three patients at a later date, and all of these showed no significant improvement on the perfusion study after PTCA. All four patients asymptomatic at 7 months following PTCA had an average 15% improvement in segmental perfusion after the procedure. In two patients symptomatic after PTCA, one showed angiographic patency and had greater than 15% improvement in perfusion, while the second showed no scintigraphic improvement (no angiographic data obtained). This preliminary study suggests that Tc-99m MIBI is an important adjunct to angiography in estimating the amount of myocardium "at risk" before and after PTCA.