Mitral valve (MV) repair has been recommended for MV diseases. Good repair requires a full understanding of the three-dimensional (3D) structure of the MV, however, currently little is known about the 3D structure of the rheumatic MV. A total of 82 cases underwent 3DTEE. Of these, 41 patients with rheumatic valvular disease (RVD) were studied intraoperatively (17 had severe mitral stenosis, 8 had severe mitral regurgitation, 16 had severe mitral stenosis coupled with regurgitation). There were 19 patients with degenerative MV disease (mitral valve prolapse [MVP] with severe regurgitation) and 22 cases with normal MV served as control subjects (CS). Compared with CS, the anteroposterior diameter, anterolateral posteromedial, annulus circumference, and annulus area of both pathological groups, i.e., the RVD and MVP groups, were understandably greater. Though the sphericity index was greater in the RVD group vis-à-vis CS, the MVP group had nearly the same sphericity index as CS. The mitral annulus of patients with RVD tended to be round. Annular unsaddling, defined as annular height to commissural width ratio (an indicator of saddle degree) less than 15%, was significantly more prevalent in the group with degenerative MV disease. Automatic dynamic analysis revealed that the parameters of annular maximum displacement and annulus area fraction (two-dimensional) were considerably decreased in the RVD group. Annular unsaddling was significantly more prevalent in the degenerative MV disease group. The mitral annulus of patients with RVD tended to be round and stiff.