Backgrounds Measurement of the vena contracta width (VCW) on 2 dimensional (2D) echo has been proposed as an accurate, quantitative method to measure mitral regurgitation (MR) severity. However, the actual VC is ovoid, not circular, therefore this method is theoretically inaccurate. We could analyze the area of vena contracta (VCA) using 3D echo and this VCA seemed to be more geometrically sound. Objectives The study was performed to test the validity of measurement of VCA for quantitation of MR by the correlation to other quantitative methods and by reproducibility. Methods We included 23 patients with MR varying in severity. The VCA was measured at the narrowest portion of color MR jet just below the valve after carefully aligning the jet into short axis view using real time 3D echo and off-line analysis system(Figure). The VCA of each patients was correlated to VCW, PISA radius, PISA regurgitant orifice area (PROA), PISA regurgitant volume (PRV) and Doppler volumetric regurgitant volume (DRV). Results Measurements of VCA were possible in all patients. VCA correlated well with VCW (r=0.86, p=0.0001), PISA radius (r=0.89, p=0.0001), PROA (r=0.80, p=0.0001), PRV (r=0.83, p=0.0001), but not as well with DRV (r=0.31, p=0.24). Intra-observer and inter-observer variability of VCA were 12.2% and 13.5% each other. Conclusions VCA is correlated well with VCW as well as PISA indices for MR quantitation, and has acceptable reproducibility. VCA measured by real time 3D echo is a new and valid method for quantitation of MR.