Transposition of the great vessels (TGV), also referred to as transposition of the great arteries (TGA), is a relatively rare congenital heart defect and the second-most common type of defect that causes babies to turn blue. Transposition means that the great vessels – the aorta and pulmonary artery – are switched so that the aorta arises from the right ventricle while the pulmonary artery arises from the left ventricle. This causes the oxygen-depleted blue blood to be pumped from the aorta to the body while the red, oxygen-rich blood is pumped out to the lungs, which is a life-threatening situation. TGV is often diagnosed even before a baby is born, or possibly right after birth due to the baby’s blue color. Babies with this condition will have rapid breathing and other signs of illness within a few days of their birth. Thankfully, effective medical treatments, including surgical interventions, can be provided with good results to help infants who are just four or five days old. A cardiac catheterization and balloon septostomy may initially be performed, followed by an “arterial switch” surgery to sever the great arteries from the heart, reverse their positions, and attach each of them to the correct ventricle.