The mitral valve was the first valve to be evaluated echocardiographically and has remained a priority of evolving echocardiographic techniques. Besides the multiple primary diseases of the mitral valve, it can also be impacted secondarily by other remote cardiac diseases. The mitral valve is the left-sided atrioventricular valve and separates the left atrium from the left ventricle. Embryologically, it forms from the endocardial cushions between the 5 and 8 weeks of development and is bicuspid, consisting of anterior and posterior leaflets (Fig. 1.1). These valve leaflets are attached to the ventricular walls by thin, fibrous chords, the chordae tendineae, which insert into small papillary muscles that are sculpted from the ventricular wall.