The mitral valve of the heart lies between the left atrium and left ventricle. Mitral valve prolapse is a common condition. If part of the valve balloons out so that the valve does not close properly, mitral valve prolapse occurs. The condition is usually asymptomatic and doesn't require treatment. Mitral valve prolapse is associated with a characteristic murmur that is detected through use of a stethoscope. Follow the links below to find WebMD's comprehensive coverage about mitral valve prolapse, including its symptoms, treatment, relationship to other heart conditions, and much more.