The normal mitral valve leaflets meet to prevent blood from flowing back into the left atrium. When the valve is weakened it may prolapse, or balloon back, into the atrium as blood is pumped by the ventricle into the aorta. Many people live with this condition without symptoms. But when a prolapsing valve allows blood to leak back into the atrium, this is called regurgitation. A regurgitating, (or leaky) mitral valve may need to be treated.