Background- Feasibility of assessing coronary blood flow (CBF) in left anterior descending coronary artery (LAD) has been documented in a number of studies. We hypothesized that nitroglycerin(NG) dilates epicardial coronary artery(ECA) with negligible effect on the resistance vessel, which determines the CBF. Therefore, even if NG can affect the CBF by its effect on the preload, dilatation of the ECA by NG reduces the CBF velocity, and the magnitude of reduction in CBF velocity after NG can reflect magnitude of ECA dilatation. Methods and results- Quantitative coronary angiography(QCA) was performed at the LAD before and after intracoronary NG(200ug) infusion in 15 patients with normal coronary angiogram. Vasodilatory reserve(VR) assessed by QCA(VRangio) was defined as (LAD diameter after NG)²/(LAD diameter before NG)². Mean values measured at the ostium and at the junction of mid and distal LAD were used for the analysis. CBF velocity was evaluated by TTE at the distal LAD during end-expiratory apnea before and 3 min after sublingual NG(NGsl). VR assessed by TTE(VRecho) was defined as (CBF velocity diameter before NGsl)/(CBF velocity after NGsl). Diastolic blood pressures before and after NGsl administration were not significantly different. There was a significant correlation between VR angio and VR echo(Figure). Conclusions- VR of the epicardial coronary artery can be assessed by the TTE and we anticipate the results of this study to be useful in the evaluation of transplantation vasculopathy