<p><span style="font-size: medium;"><strong>Background:</strong> The fractional flow reserve (FFR) has been established as a physiological tool for the assessment of coronary ischemia. The instantaneous wave-free ratio (iFR) is an alternative pressure-derived physiologic index from the diastolic wave-free period in stable conditions. The hyperemic iFR (h-iFR) may represent a diagnostic tool; however, its diagnostic performance is unclear. Thus, we aimed to assess the diagnostic performance of the h-iFR compared with the conventional whole-cycle FFR. </span></p><p><span style="font-size: medium;"><strong>Methods:</strong> Fifty consecutive lesions, which were diagnosed as 50-75% stenosis by coronary angiography, were analyzed regarding the h-iFR and FFR during the intravenous administration of adenosine using a pressure wire. The h-iFR and FFR were calculated via automated algorithms.</span></p><p><span style="font-size: medium;"><strong>Results:</strong> Twenty-two stenoses were positive (FFR ≦0.8), and 28 stenoses were negative (FFR &gt;0.8). The slope of the regression line was 1.28 in the positive group and 1.61 in the negative group. The FFR and h-iFR values ranged from 0.64 to 0.80 (0.75±0.04) and 0.52 to 0.82 (0.66±0.07), respectively, in the positive group and 0.81 to 1.02 (0.90±0.05) and 0.69 to 1.02 (0.87±0.08), respectively, in the negative group. The means of the differences between the FFR and h-iFR were 0.027 and 0.090 in the FFR positive and negative groups, respectively. </span></p><p><span style="font-size: medium;"><strong>Conclusions:</strong> The hyperemic iFR, which is calculated using the diastolic phase and exhibited a larger dynamic range than the FFR, especially in FFR-positive stenosis, may be a better physiological tool than the cardiac full-cycle FFR in the evaluation of coronary ischemia.</span></p><strong><br clear="all" /> </strong>