Background: The optimal cutoff values of vena contracta (VC) width for assessing functional tricuspid regurgitation (FTR) severity from different views have not been demonstrated. Methods: Real-time 3D (RT3D) full-volume and color Doppler images were obtained and 2D Doppler echocardiography was performed in 40 patients with various degree of FTR and in sinus rhythm. Using cross-sectional image of VC on RT3D color Doppler image, VC widths were measured parallel to the septal-lateral (SL) and antero-posterior (AP) directions in a mid-systole frame. Effective regurgitant orifice area (EROA) was measured using proximal isovelocity surface area obtained from RT3D color Doppler image with baseline shift and FTR maximal velocity. Right ventricular (RV) volumes and ejection fraction were measured, and geometric analyses of tricuspid valve apparatus and RV were performed using RT3D images. Results: SL VC width was significantly smaller than AP VC width (-0.53 짹 0.40 cm, p<0.001). By multiple linear regression analyses, SL VC width was determined by SL annulus diameter (p=0.004) and tenting angle of septal leaflet (p=0.008), while AP VC width was by tenting angle of anterior leaflet (p<0.001), AP annulus diameter (p=0.002) and annulus to apex distance (p=0.27). EROA was mainly determined by SL annulus diameter (p<0.001), tenting angle of septal leaflet (p=0.001) and SL RV inlet dimension (p=0.015). EROA significantly correlated with SL (r=0.807, p<0.001) and AP (r=0.747, p<0.001) VC widths, and VC area (r=0.829, p<0.001). The best cutoff values of SL and AP VC widths for EROA ��� 0.2 cm² were 0.7 cm (sensitivity of 94%, specificity of 75%) and 1.3 cm (sensitivity of 94%, specificity of 83%), respectively, using ROC curve analyses. The best cutoff values of SL and AP VC widths for EROA ��� 0.4 cm² were 0.9 cm (sensitivity of 88%, specificity of 84%) and 1.6 cm (sensitivity of 100%, specificity of 84%), respectively. Conclusions: VC widths and area are good indices for assessing FTR severity. Different cutoff values should be applied according to different 2-dimensional views, since the VC shape is usually ellipsoidal with long AP direction.