This study concerns 51 cases of mitral valve prolapse demonstrated on bidimensional 4 cavities sonography according to Gilbert's criteria and aims to determine the frequency of the associated valvular involvement, anatomically with sonography and functionally with the Doppler test. Sonography demonstrates a tricuspid valve prolapse in 79 p. cent of the cases and an aortic valve prolapse in 10 p. cent. The Doppler test demonstrates a tricuspid leakage in 52 p. cent of the cases, a pulmonary leakage in 62 p. cent, and an aortic leakage in 18 p. cent. The myxoid degeneration found in 60 p. cent of the cases is a major factor in the occurrence of complications, especially progressive cardiac insufficiency (A). The myxoid degeneration defines therefore the "isolated prolapse disease" as opposed to "the prolapse without myxoid degeneration" which is a pure sonographic entity and probably a variation of the normal (A). This cardiac insufficiency occurs late during the 6th or 7th decade and is due to mechanical factors: prolapse, chords rupture and annular dilatation.