The flow of the right upper pulmonary vein , will be recorded during the reverse wave. The flow in pulmonary veins (average of 3 different measurements) will be recorded additionally. The transmitral A wave duration will also be measured, with the Pulsed Doppler sample volume placed at the level of the mitral annulus (average of 3 different measures). The time difference between the Ar-A (reverse pulmonary venous - transmitral flow A wave) will be calculated .