Mitral valve prolapse and regurgitation. When your heart is working properly, the mitral valve closes completely during contraction of the left ventricle and prevents blood from flowing back into your heart's upper left chamber (left atrium).he bulging may keep the valve from closing tightly. When blood leaks backward through the valve, it's called mitral valve regurgitation. This may not cause problems if only a small amount of blood leaks back into the atrium.