As a result, blood in the left ventricle backs up into the left atrium during ventricular systole. Over time this will lead to left atrial dilation/hypertrophy, increased pulmonary vascular pressure and volume and pulmonary edema. The most common cause is mitral valve prolapse. Other causes include ruptured papillary muscle dysfunction, infective endocarditis, dilated cardiomyopathy, myocarditis, connective tissue disorders, nonbacterial endocarditis.