Transposition of the great arteries

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Transposition of the great arteries is a reversal of the normal connections of the aorta and the pulmonary artery with the heart.

The aorta and pulmonary artery are reversed, which causes oxygen-poor blood to be circulated to the body and oxygen-rich blood to be circulated between the lungs and the heart and not to the body.
Symptoms are apparent at birth and include severe cyanosis (a bluish discoloration of the lips and skin) and difficulty breathing.
The diagnosis is based on echocardiography.
Surgery is done during the first few days of life.

(See also Overview of Heart Defects.)
Oxygen-poor blood returning from the body flows from the right atrium to the right ventricle as usual, but then flows to the aorta and the body, bypassing the lungs. Oxygenated blood travels back and forth between the heart and lungs (from the lungs to the pulmonary vein, then left atrium and ventricle, then the pulmonary artery) but is not transported to the body.
The body cannot survive without oxygen. However, infants with this heart defect may survive briefly after birth because the foramen ovale (a hole between the right and left atria) and the ductus arteriosus (a blood vessel connecting the pulmonary artery with the aorta—see Normal Fetal Circulation) are still open at birth. These openings allow oxygen-rich blood to mix with oxygen-poor blood, sometimes supplying enough oxygen to the body to keep the infant alive. Once the ductus closes, as it normally does after birth, very little blood flows to the lungs in infants with this defect and if the defect is not repaired immediately, the infant will die.
Transposition of the great arteries can also be accompanied by another heart defect, ventricular septal defect (a hole in the wall separating the two lower heart chambers), which may actually be helpful by allowing more mixing of oxygen-rich and oxygen-poor blood.