The ductus arteriosis (also spelled ductus arteriosus) is a shunt—a diversionary channel or flow--that allows blood to cross between the pulmonary artery and aorta. The shunt of blood from the pulmonary artery to the aorta through the ductus arteriosis, also a shunt of blood from the pulmonary to the systemic circulation, is normal and necessary during fetal development. At birth, changes in the pressures brought about by respiration effectively reverse the shunt through the ductus arteriosis and ultimately result in a closure of the shunt. The ductus arteriosis usually closes completely within eight weeks to six months of birth. In a normal adult, the closed ductus arteriosis becomes the ligamentum arteriosum that runs between the aortic arch and the left pulmonary artery.

In a small number of cases—about 1 in 2,200 births—the ductus arteriosis remains open (patent) and a patent ductus arteriosis...