This chapter deals with mitral valve (MV) disease. Mitral stenosis is obstruction of left ventricular inflow at the level of the MV, as a result of structural abnormalities of the MV apparatus that limit proper opening during diastole. Mitral annular calcification is a degenerative process, and is a common incidental finding in the elderly. Rheumatic carditis is the commonest cause of mitral stenosis in both developed and developing countries. Mitral regurgitation (MR) is the most commonly encountered valvular lesion in modern clinical practice. Primary MV prolapse syndrome (MVPS) refers to a disease spectrum with frank myxomatous degeneration at one extreme. The transesophageal echocardiography (TEE) variables used in the assessment of MR severity can be classified as semi-quantitative or quantitative. The vena contracta (VC) refers to the narrowest portion or neck of the regurgitant jet, which occurs at or just beyond the regurgitant orifice.