Background and Method : To evaluate the acute effect of nicorandil on the myocardial perfusion, total 39 patients with effort angina, who were proven to have significant stenosis on coronary angiogram and reversible perfusion defects in exercise Thallium-201 single Photon Emission Computed Tomography(SPECT) after placebo administration, underwent exercise T1-201 SPECT at 30 minutes after single oral administration of nicorandil of two different doses 7 days after the reference study. Patients were divided randomly into 2 groups depending on their doses of nicorandil(group 1 : 10mg ; n= 19, group 2 : 20mg : n=20). Results : There were no differences in hemodynamic variables at rest and peak exercise before and after nicorandil administration in group 1. However, in group 2, heart rate at rest increased from $80{pm}14;to;85{pm}17$ beats/min(p<0.05) and systolic, diastolic and mean blood pressures at rest decreased from $141{pm}21$, $93{pm}12;and;109{pm}14mmHg;to;124{pm}16,;85{pm}11,;and;98{pm}12mmHg$, respectively(p<0.05), but there were no differences in heart rate and blood pressures at peak exercise before and after niorandil. In group 1, total Thallium defect extent in stress image and total reversible ischemic area were significantly decreased after nicorandil from $38{pm}5%,;19{pm}3%;to;26{pm}4%,;11{pm}2%,$ respectively(p<0.05) In group 2, total Thallium defect extent of stress image was decreased significantly from $22{pm}3%;to;18{pm}3%$ after nicorandil 20 mg(p<0.05). but mild decrease of reversible ischemic area 434 not reach the statistical significance(p>0.05). Conclusion : These results revealed that single dose(10 or 20mg) oral administration of nicorandil significantly reduced total Thallium defect extent in stress images of the exercise T1-201 SPECT(p<0.05) in patients with effort angina.