It occurs due to ill formed heart during pregnancy. It can be identified in newborns and has to be treated as soon as possible. The defect can either be in the heart walls, the septa, the valves or the lining muscles. It is a birth defect and effects the pumping of the heart resulting in low oxygenated blood to the body. The term is actually an umbrella term under which covers conditions like vascular septal defect, atrial septal defect, teratology of fallot, stenosis, transposition and more. The condition is more common in premature children.