The Doppler spectrum diagnosis of mitral stenosis includes two stages: positive diagnosis and diagnosis of gravity. The positive diagnosis rests on the increase of the maximal velocity of the transmitral flow, the persistence of this acceleration during the entire diastole with decrease of the deceleration gradient, more marked when the stenosis is narrower, and the enlargement of the spectrum. The diagnosis of gravity rests on the measurement of the mean gradient by applying Bernouilli's equation and the point by point quadratic transformation of the transmitral velocity curve obtained by Doppler and the measurement of the mitral area either by measurement of the half-decrease time in pressure or by applying the continuity equation. This last method advocated by Nakatani is particularly interesting in case or significant aortic insufficiency which often invalidates the application of T1/2.