In the normal heart, two arteries emerge from the heart:
The pulmonary artery carries blood from the right ventricle (lower right chamber) to the lungs, where it picks up oxygen and the aorta carries blood from the left ventricle to the rest of the body. In truncus arteriosus, a single blood vessel emerges from the heart, and then branches into a pulmonary artery and an aorta. This single vessel, called the truncus arteriosus, emerges from both ventricles – specifically from the hole in the wall between the two ventricles, called the ventricular septal defect (VSD).