The heart’s lower-right chamber (the right ventricle) and lower-left chamber (the left ventricle) are divided by a wall called the septum. The septum ensures that blood does not mix between the right and left ventricles.

One feature of truncus arteriosus is a large hole in the septum between the two ventricles (called a ventricular septal defect). This lets oxygen-poor blood mix with oxygen-rich blood. When this mixture of blood is pumped into the body, it may cause the lips, fingers, and toes to appear blue, a condition called cyanosis.

Truncus arteriosus also causes the arteries to form abnormally. Instead of the pulmonary artery connecting to the right ventricle and the aorta connecting to the left ventricle, the heart has just one big artery that connects to both ventricles. The pulmonary arteries then branch off this common artery.

What are the symptoms?

The defect may cause too much blood flow to the lungs and force the heart to work too hard. Babies born with truncus arteriosus have trouble breathing, feeding, and growing normally.

How is it treated?

Surgery to correct this condition is usually done in infancy. The pulmonary arteries are separated from the common artery and attached to the right ventricle with a tube. The hole in the septum is usually covered with a patch.