Hi there There is the natural response of the body, and its organ system to compensate, or at least to attempt tom compensate...to any form of changes in the normal homeostatic condition. This goes the same with the heart. If you have a leaky atrioventricular valve (most presumably the mitral valve, which is the gate between the left atrium and the left ventricle), The heart will compensate in the ff. way: If the mitral valve regurgitation is severe, even though the left ventricle would increase the heart rate and contractility to maintain the normal cardiac output, it will pump back blood into the left atrium. THE LEFT VENTRICLE USUALLY DILATES OR BECOME ENLARGED. If the left atrium is then receiving more blood than the usual inflow, (this time some blood also comes back from the left ventricle,) THE LEFT ATRIUM MAY ALSO GET ENLARGED. The usual case is, for mitral regurgitation, the left atrium does not enlarge significantly, but the pressure of the blood gets transmitted back to the pulmonary vein, and the pulmonary system. Therefore, PULMONARY HYPERTENSION might develop. If this is severe enough, blood might flood the lungs to cause PULMONARY EDEMA. If this goes any worse, it will go back to the right ventricle causing RIGHT VENTRICULAR FAILURE .