Background and Aim: Noninvasive measurement of coronary vasomotion is important for the evaluation of patients with coronary artery disease (CAD). The aim of this study was to investigate the use of free-hand 3D echocardiography (3DE) with rotational geometry for assessing epicardial coronary artery vasodilation. Methods: Forty-five subjects were studied: 29 subjects (age 51짹12 years, M:F=14:15, Control group) with normal coronary angiogram and 16 patients with multivessel CAD(age 60짹12 years, M:F=9:7, CAD group). After obtaining the tubular color flow signals of distal left anterior descending coronary artery(LAD) using an ultra-band transducer (5-12 MHz) with a special preset program of a low velocity range, the peak(PDV), mean diastolic velocity (MDV) and velocity time integral(VTI) were measured before and after sublingual nitroglycerin (NTG) (0.3 mg).In all subjects, using a 3DE unit with magnetic tracking system (TomTec Imaging Systems) linked to the conventional 2D ultrasound system(Sonos 7500) 3DE image acquisition and reconstruction of the distal LAD flow was performed before and after sublingual nitroglycerin (NTG). Quantitative analysis of coronary vasodilation was performed on cross-sectional images. Results: 1.The % change of PDV, MDV and VTI after NTG was 41.3짹14.0%, 37.9짹13.8% and 40.3짹18.2 % in Control group and 23.0짹13.9 %, 19.1짹11.5 % and 26.1짹12.4 % in CAD group.(p<0.05, versus Control group, respectively) 2. The distal LAD diameter on coronary 3DE increased from 2.28짹0.79mm to 3.32짹1.07mm (52.3짹28.5%) in Control group and from 2.36짹0.65mm to 2.89짹0.81mm(23.7짹23.9%) in CAD group after NTG.(p<0.005 versus Control group) 3.The magnitude of vasodilation correlated with the % change of PDV (r=0.516, p<0.005), MDV (r=0.519, p < 0.005) and % VTI (r=0.392, p=0.008). Conclusion: These data indicate that vasodilation after NTG administration is reduced in the advanced atherosclerosis and can be noninvasively measured. The 3D reconstruction of the distal LAD flow using free-hand 3DE with rotational scanning is a promising noninvasive technique to study coronary vasomotor function.