Background: Coronary flow reserve (CFR) is known as an index of the microcirculatory function of myocardium. Before percuatneous coronary intervention (PCI) in coronary artery disease, prediction of CFR (CFRpred) of the myocardium assumed without epicardial stenosis may be valuable for evaluating the degree of microvascular integrity before PCI. We evaluated the feasibility of CFRpred assessed before PCI by comparing the CFRreal after PCI. Methods: Sixteen patients (60짹11 years) performed PCI and undergone the study of coronary pressure and hemodynamics by intracoronary pressure wire and Doppler wire were studied. Before PCI, we assessed CFRpred which was calculated as the ratio of baseline[Pd �� Tmn �� {(Pd-Pcw)/(Pa-Pcw)}/(Pd/Pa)]) and hyperemia[Pd �� Tmn �� {(Pd-Pcw)/(Pa-Pcw)}/(Pd/Pa)])(Pd: mean coronary pressure of distal site of the lesion, Tmn: mean transit time, Pcw: coronary wedge pressure, Pa: mean aortic pressure). We compared the CFRpred with CFRreal assessed by thermodilution method. We devided the patients into two group (A: the patients with CFRreal < CFRpred, n=10, B: the patients with CFRreal ��� CFRpred , n=6). Results: There was significant between CFRpred and CFRreal (r=0.639, p=0.008). The number of the difference between both parameters more than two standard deviation was 6%. The peak CK-MB after PCI was not different between the two groups. The baseline IMR was significantly lower in group A than group B (29.3짹6.8 vs. 50.7짹12.7, p=0.001). The baseline IMR significantly decreased in group A after PCI compare to before PCI (42.1짹19.3 vs. 29.3짹6.8, p=0.015). Conclusion: .CFRpred before PCI was feasible in predicting the CFR after PCI in angina patients. The abnormal CFR after PCI was related with lowering baseline IMR which might be related compensatory hyperemia during PCI or no recovery of autoregulation.