Mitral valve failure. Coloured magnetic resonance imaging (MRI) scan through the chest of a patient with heart valve failure of the mitral valve. This condition is where the mitral valve is failing to properly regulate the flow of blood through the heart, leading to mitral regurgitation. The heart and its valves are at upper centre. The mitral valve is between the heart's left atrium and the left ventricle The valves between the chambers of the heart prevent blood flowing backwards after it is pumped out. If the valves are damaged or defective, then blood can flow back through the heart (regurgitation), resulting in decreased blood flow to the rest of the body and increased work for the heart.