English: What is mitral valve disease? If the mitral valve doesn't open all the way during diastole, it's known as mitral stenosis. If it doesn't close all the way during systole, it's called mitral regurgitation. Sometimes the valve leaflet can fall backward into the atrium, in which case it's known as mitral prolapse. This video covers the pathophysiology, complications, as well as signs and symptoms for mitral valve disease.