Currently, clinical assessment of mitral regurgitation (MR) makes the use of 2D color Doppler imaging for the estimation of the vena contracta (VC) and of the effective regurgitant orifice area (EROA)..Since the anatomic regurgitant orifice (ARO) has a 3D shape and it's not circular, it cannot be accurately represented by these 2D parameters. We developed a novel semiautomated method for 3D ARO segmentation and quantification using 3D transesophageal echocardiographic (TEE) datasets, and validated it vs manual planimetry on a set of 25 patients with mild to severe MR. ARO 2D projected area and circularity index (CI) correlated well with planimetry results (r2=0.77 and 0.90 and bias of -0.02 and 0.02, respectively). In 19/25 patients ARO planarity index was less than 0.9, confirming its 3D morphology. Only 1/25 patients exhibited an almost circular ARO (CI > 0.92), while 24/25 patients had more elongated orifices (CI<;0.8). In conclusion, volumetric quantification of 3D ARO is feasible, and the results confirm the potential of this technique for the estimation of real 3D ARO shape. The proposed method could be a useful alternative for the assessment of patients with MR, given the intrinsic shape of the ARO and the limitations present in current approaches.