To clarify the value of transesophageal Doppler echocardiography in evaluating coronary flow reserve in patients with a stenosis in the left anterior descending coronary artery (LAD), we studied thirty seven patients with a stenosis in the LAD using transesophageal Doppler echocardiography. Coronary blood flow velocity was measured by transesophageal Doppler echocardiography in the proximal portion of the LAD. Measurements were taken both in a baseline condition and after dipyridamole infusion (0.56 mg/kg in 4 min). Indexes of coronary flow reserve were expressed by dipyridamole/baseline ratios of peak diastolic velocity and mean diastolic velocity (P-CFR, M-CFR). Angiograms of each lesion were analyzed by the quantitative coronary angiography, and significant stenosis was defined as a 50% or greater luminal diameter narrowing. Twelve of the 37 patients had a significant stenosis in the LAD (group A), and the remaining 25 patients did not (group B). In the baseline condition, there were no significant differences in coronary blood flow velocities between the two groups, after dipyridamole infusion, however, coronary blood flow velocities were significantly higher in group A patients than group B patients. Indexes of coronary flow reserve were significantly lower in group B patients than group A patients. P-CFR and M-CFR ratio of 2.5 yielded optimal separations of values for coronary flow reserve. The sensitivity and specificity of P-CFR to the significant stenosis in the LAD were 88% and 83%, respectively, and those of M-CFR were 84% and 92%, respectively. These results indicate that dipyridamole stress transesophageal Doppler echocardiography is a useful and highly sensitive technique for detecting a significant stenosis in the LAD.