Blue- baby syndrome, or blue baby is usually caused by a heart defect which laymen often call "a hole in the heart". Normally, oxygenated blood from the lungs is separated from deoxygenated blood from other tissues. A defect in the heart ventricle walls can allow deoxygenated blood to mix with the blood from the lungs. The resulting blood going through the aorta has less oxygen than usual, and the baby looks blue. An operation is usually done to fix this