Tricuspid atresia is a type of congenital heart disease in which the valve between the right atrium and right ventricle fails to develop.

Blood that returns from the body to the right atrium cannot directly enter the right ventricle, and must pass through a hole in the atrial septum (atrial septal defect) into the left atrium and then the left ventricle.

There are several anatomic variations that influence the symptoms and course of treatment in any given patient.

There may be a hole in the ventricular septum, called a ventricular septal defect (VSD).

The aorta and pulmonary artery may be normally positioned and aligned with the appropriate ventricle (as shown in illustration), or they may be reversed, a condition called transposition of the great arteries.

If the ventricular septal defect is small or absent, and the great arteries are normally positioned, blood flows from the left ventricle out the aorta to the body. In this situation very little, if any, blood can get to the lungs resulting in very low oxygen levels in the infant.

In a newborn, blood can reach the lungs to pick up oxygen as long as a connection between the aorta and pulmonary artery called the ductus arteriosus remains open. The “ductus” is an important vessel while the baby is still in the womb because it allows the blood from the baby's heart to return to the placenta, which does the job of the lungs before birth.

This vessel is exquisitely sensitive to oxygen, so when the baby is born, it typically narrows down (or closes completely) after 24 to 48 hours in response to the oxygen levels in the air breathed by the child. An intravenous medication called prostaglandin (PGE) can keep this important vessel open after birth.

If a ventricular septal defect is present and the great arteries are in their normally related position, blood from the left ventricle can reach the lungs through the ventricular septal defect. This channel is often very narrow, and the right ventricle very underdeveloped, so a less than normal amount of blood goes to the lungs.

Finally, if there is transposition of the great arteries, blood reaches the lungs easily because the pulmonary artery is directly connected to the left ventricle. But blood can only reach the body through the ductus arteriosus or the ventricular septal defect if there is one.