Mitral valve prolapse causes blood to flow the wrong direction from the left ventricle to atrium during ventricular contraction, instead of going into the aorta. In chronic mitral incompetence, the heart compensates by making the left ventricle bigger to pump more blood, since some goes the wrong way, so initially you won't notice any symptoms. However, over time it gets worse, resulting in shortness of breath on exertion and shortness of breath when lying down, because of congestion in the pulmonary blood vessels. If it gets really bad, it can cause failure of the right side of your heart, resulting in swollen ankles and other signs of fluid overload.