The mitral valve in the heart lies between the left atrium atrium. And the left ventricle opens when the atrium pumps blood into the chamber and closes when the ventricle pumps blood into the body. The closure prevents blood from returning to the atrium. Blood flows back into the atrium due to Leaky mitral valves Blood is not being pumped out of the heart properly. and the upper atrium cannot be filled in the next round. Blood may rush to the right side to the lungs. and fills the lungs with fluid The left ventricle has to do more work to move the blood. Later, it can cause heart failure.