Mitral valve prolapse (MVP) is a condition in which the mitral (bicuspid) valve extends back into the left atrium when the heart beats, causing blood to leak from the atrium to the ventricle. It may be due to genetic factors or a bacterial infection, caused by Streptococcus bacteria. Mitral valve prolapse affects up to six percent of the U.S. population. Surgery is sometimes required to repair a valve, although most people do not require any treatment.