Bluish discolouration of the skin due to lack of oxygen in the blood. Mostly the result of an existing congenital heart defect. In this case, part of the oxygen-depleted blood does not flow into the lungs to take up oxygen there, but instead flows through a hole in the septum from the right into the left part of the heart and directly back into the systemic circulation. Can also occur as a result of narrowing (stenosis).
