The effect of nicorandil on myocardial perfusion in ischemic heart disease was studied using exercise-load Tl-201 myocardial SPECT (Ex-SPECT). ExSPECT was carried out in 12 patients with previous myocardial infarction (OMI) and 9 with angina pectoris (AP) before and after administration of nicorandil 15 mg/day, for three or more weeks; %Tl uptake and the washout rate in infarcted or ischemic areas were calculated from short axial images using the Bull's eye method. In the OMI group, %Tl uptake and washout rates in the infarction areas improved significantly from 52.4% and 0.25 before nicorandil to 60.4% and 0.38 after nicorandil. In the AP group, too, %Tl uptake and washout rates showed a significant improvement from 56.9% and 0.10 before to 69.1% and 0.33 after administration of nicorandil. Six subjects who had not received the drug, and who showed negative washout rates, had high improvement rates when nicorandil was administered, suggesting that the drug could increase myocardial perfusion during exercise loading as well as suppressing coronary spasm. Ex-SPECT was carried out in 4 subjects before and after the administration of nicarandil and after subsequent surgical treatment (PTCA or CABG) and the effects of the two therapies were compared. The washout rate was improved from 0.01 to 0.34 by the administration of nicorandil, and a notable increase in coronary artery blood flow was achieved compared to the level after surgical treatment, i.e. 0.50. It is concluded that normal dosages of nicorandil have a powerful direct effect of dilating the coronary arteries without any influence on preload or afterload.