Tetralogy of Fallot occurs when the right side of the heart does not develop properly while a baby is in the mother's womb. A French physician, Etienne Fallot first described it, in 1888. The cause of the problem is not understood. The parts of the heart affected are the pulmonary valve, right ventricle and the ventricular septum.

Total anomalous pulmonary venous return (TAPVR) is a heart defect in which one or all of the pulmonary veins between the lungs and heart are not properly connected.

Complete transposition of the great arteries (TGA) occurs when the aorta, which normally comes off the left ventricle and pumps red blood to the body, arises from the right ventricle(1) and pumps blue blood returning from the body back to the body bypassing the lungs completely. The pulmonary artery, which normally arises from the right ventricle and pumps blue blood to the lungs, arises from the left ventricle (2) and sends red blood returning from the lungs right back to the lungs. Essentially

Tricuspid atresia occurs when the tricuspid valve fails to develop while the baby is in the womb. This problem is quite rare, affecting 1 in 15,000 births, and it occurs equally in boys and girls.

Truncus arteriosus occurs when the great arteries do not develop normally while the baby is in the mother’s womb. In this defect, instead of two large vessels that arise from the base of the heart, there is only one vessel. It is one of the rarer forms of congenital heart disease comprising about 1% of congenital heart defects and is slightly more common in boys than girls. It is also slightly more common in children of diabetic mothers.