The Mitral Valve is a structure on the left side of the human heart that regulates the flow of oxygenated blood into the Left Ventricle and also helps maintain the pressure within the Left Ventricle when the blood gets pumped to the rest of the body from the Left Ventricle. Pathology of the Mitral Valve often manifests through structural changes in the anatomy. Assessment of Mitral Valve pathology as well as determination of specific interventions require quantification of various structures of the Mitral Valve and one of these structures of interest is the Mitral Valve annulus. Three dimensional echocardiography is a popular imaging technique that clinicians use for volumetric quantification of cardiac structures - but manual quantification is cumbersome and subjective. In this paper we describe a semi-automated approach for maximum-a-posteriori estimation of the Mitral Valve annulus from three-dimensional echocardiography images using a simple analytic shape model coupled with a Näive Bayes classifier. We validate our approach against manual annotations on over 15 real patient cases with an average localization error ≤ 2.59 mm.