Aims : It is already known that the value of Fractional flow reserve(FFR) in infarct myocardium is influenced by the amount of scar tissue. We test the hypothesis that the amount of scarred myocardium can be measured with coronary pressure wire if baseline of Pd/PAo (Pd : the pressure of distal segment of stented infart related artery, PAo : the pressure of aorta) is set to a same value in infarct related artery. Methods : 23 patients were enrolled in this study. After successful PCI in infarct related artery, the coronary pressure wire was inserted in infarct related artery and then the partial occlusion by an under sized balloon inflation in the stented segment was controlled in order to set the value of baseline Pd /PAo to 0.8. The final Pd/PAo under maximal hypermeia was acquired by the intravenous adenosine infusion. The drop of the final Pa/PAo from the baseline value (0.8) was defined as "Vasoreactivity Index(VARI)". All patients also underwent cardiac MRI. 4 short axis slices of LV were analyzed to determine both Infarct area and infarct segment myocardium (Fig1). Infarct ratio in infarct segmented myocardium (IRIS) was defined as the ratio of infact area to the area of infarct segmented myocardium. Results : A significant inverse correlation was found between VARI and IRIS (R=0.7474, P<0.001)(Fig2). The 0.1 cutoff value of VARI was valid for distinguishing more than 50% IRIS from less than 50% IRIS. (71.0짹17.9% vs 27.5짹18.8%)(Fig 3). The sensitivity and specificity of the cutoff value are 100% and 93%, respectively. Conclusion : The present date showed that VARI seems to be a powerful predictor of the proportion of scarred myocardium in myocardial infarction.