Transposition of the great arteries (TGA) is a type of congenital heart defect in which the two great arteries (the pulmonary artery and the aorta) are in reversed (transposed) locations. This reverses circulation in the heart. Normally, oxygen-rich blood travels through the aorta to nourish the cells and tissues, while oxygen-poor blood travels through the pulmonary artery on its way to the lungs for fresh oxygen.

By contrast, TGA results in two kinds of parallel circulation. Oxygen-poor blood from the body is pumped back out to the body through the aorta, while oxygen-rich blood is pumped back to the lungs through the pulmonary artery.

Survival depends on the presence of other heart defects that allow some mixing of oxygen-rich and oxygen poor blood. Even with other defects, however, the baby will likely not be getting sufficient oxygen from the blood. As a result, the infant will often be born with a bluish tone (cyanosis) to the skin, lips, nails and other parts of the body (blue baby).

The other defects that might be present with TGA include a hole in the muscular wall between the heart’s upper chambers (an atrial septal defect) or a hole in the wall between the lower chambers (a ventricular septal defect). Alternatively, the young patient may be born with a patent ductus arteriosus – a condition in which the prenatal channel between the aorta and the pulmonary artery (ductus arteriosus) remains open (patent) at birth. Typically, newborn babies with TGA are given a drug that keeps the ductus arteriosus open to encourage the flow of oxygen-rich blood to the body.

To correct any heart-associated defects, surgery is generally performed in the early days following birth. Anyone who has TGA must have heart surgery early in life to survive, according to the American Heart Association.