 It divides the distal part of the truncus into two vessels, the aorta and pulmonary artery, which lie side by side above, but near the heart the pulmonary artery is in front of the aorta.Failure of the truncus arteriosus to close results in the condition known as persistent truncus arteriosus, a rare congenital heart defect.This is often just referred to as "truncus arteriosus".