The ductus arteriosus is a blood vessel in a fetus that connects the pulmonary artery, which carries blood to the lungs, and the aorta, which carries blood to the body, so that blood flow bypasses the lungs. Normally, this blood vessel closes at birth as the baby starts breathing. But if the vessel does not close, it is known as a patent (open) ductus arteriosus (PDA).

A patent ductus arteriosus allows some oxygen-rich blood to flow from the aorta back into the pulmonary artery and to the lungs instead of to the rest of the body. Because some of the blood intended for the body returns to the lungs, the left side of the heart has to pump harder to get enough blood to the body. This can enlarge and weaken the heart.

Some babies do not have symptoms from a patent ductus arteriosus. But this abnormality often causes symptoms, such as poor feeding and shortness of breath. An older child may develop heart failure or an infection of the heart’s inner lining (infective endocarditis). How bad the symptoms get and whether complications develop depend on how much blood flows through the ductus.

Treatment for a patent ductus arteriosus might be medicine that helps close the blood vessel. Or a doctor will insert a small closure device into the heart during a heart catheterization. This prevents blood from flowing into the lungs. If a heart catheterization can’t be done, a surgeon might operate to close the PDA.