Mitral Valve Atresia is a rare congenital heart defect in which the mitral valve of the heart does not develop correctly. The mitral valve normally consists of two leaflets and associated supporting structures. The job of the mitral valve is to allow passage of oxygenated blood from the left atrium to the left ventricle during the relaxation phase of the heart cycle and to keep blood from flowing back from the left ventricle to the left atrium during the contraction phase of the heart cycle. In mitral valve atresia, there is severe reduction or no flow of blood across the mitral valve. When atresia occurs, blood from the left atrium of the heart does not flow to the left ventricle, causing the left ventricle to become small and underdeveloped. Infants surviving into adulthood may develop problems with their heart functioning later in life due to worsening of the condition.Infants with mitral valve atresia have the following signs: difficult or rapid breathing, shortness of breath, cool and clammy skin, blue tinted skin, lips, and nail beds (cyanosis), and difficulties feeding. Chest x-ray, electrocardiogram, echocardiogram, cardiac catheterization, and cardiac magnetic resonance (MRI) imaging are used to diagnose this condition.