Transposition of the great arteries (TGA) is when the two major arteries leaving the heart are connected to the wrong ventricles, the lower pumping chambers of the heart. The result is that blood containing oxygen from the lungs is pumped back into the lungs. Blood that lacks oxygen, which is necessary to nourish the body, is pumped throughout the body.

The heart consists of four chambers. There are two upper chambers, called atria, where blood enters the heart; and the two lower chambers, called ventricles, where blood is pumped out of the heart. The flow between the chambers and between the arteries is controlled by a set of valves that act as one-way doors.

The heart also can be viewed as two side-by-side pumps with one side — an atrium and a ventricle with valves connecting them to blood vessels — pumping blood into the lungs and the other side pumping blood from the lungs back to the body.

Blood is pumped from the right side of the heart up through the pulmonary valve and the pulmonary artery to the lungs. In the lungs, blood is filled with oxygen. From the lungs, the blood travels back down to the heart’s left atrium and left ventricle. Then, it’s pumped through a big blood vessel called the aorta to the rest of the body.

A baby with transposed arteries is blue, or cyanotic, shortly after birth. The blueness doesn’t go away even if the baby is given extra oxygen. For a baby with transposed arteries to survive, blood flow between the right and left sides of the heart must be increased. These infants rarely survive without surgical intervention so it is extremely rare for a person to grow to adulthood without treatment.

Surgical atrial septectomy and balloon atrial septostomy are two palliative therapies for TGA. Physiological procedure (atrial switch operation) and anatomic repair (arterial switch operation) are also available treatments. The survival rate for infants with transposition of the great arteries today is greater than 90%.