Background: Intravascular ultrasound (IVUS) imaging parameters have been suggested as criteria to determine coronary lesion significance before intervention. However, there has not been a systematic examination of combined anatomic and physiologic data in the same patients with coronary artery disease. Methods and Results: To examine the relation between coronary flow reserve and IVUS parameters, 41 patients with intermediately severe coronary artery stenoses had measurements of coronary flow velocity (0.014-inch Doppler flow wire), coronary flow velocity reserve (CVR) (hyperemic/basal mean flow), IVUS imaging (2.9F, Cardiovascular Imaging Systems, Inc.), and quantitative coronary angiography before intervention. Correlations between physiologic and anatomic parameters were performed by simple regression. Results were also examined by patient subgroups with CVR >1.8 or <1.8 to assess differences in IVUS parameters. The angiographic percent diameter stenosis was 52% ± 17% (range 18% to 95%). Mean CVR was 1.88 ± 0.56 (range 0.9 to 3.18). IVUS minimal luminal diameter (r = 0.312, p = 0.047) and angiographic percent stenosis (r = 3.05, p = 0.052) were weakly related to poststenotic CVR. Comparing patients with CVR <1.8, IVUS reference segment area, IVUS lumen area, and angiographic percent diameter stenosis was higher (17.7 ± 0.3 vs 12.9 ± 4.4 mm², p < 0.05; 6.20 ± 3.76 vs 4.34 ± 2.00 mm², p < 0.05; and 60% ± 14% vs 46% ± 17%, p < 0.01, respectively) than in the group with CVR >1.8. Conclusions: Despite a precise determination of cross-sectional vessel areas and absolute dimensions by IVUS, single tomographic measurements did not correlate well with coronary physiologic responses. These data suggest that the physiologic data may be complementary to anatomic quantitative IVUS, enhancing information for coronary interventional decision making. (Am Heart J 1998;135:988-94.)