Truncus arteriosus is a type of congenital heart disease in which a baby is born with one large blood vessel—normally there are two—that receives blood from both the heart's ventricles. This single blood vessel mixes oxygen-rich blood with oxygen-poor blood. Oxygen-rich blood and oxygen-poor blood normally remain in two separate blood vessels in the heart.

Treatment is a surgery that divides the single large blood vessel into two separate blood vessels so that blood can circulate properly.