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 PDA 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 may have 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 PDA. But this problem may cause symptoms, such as poor feeding and shortness of breath. How bad the symptoms get and whether complications develop depend on how much blood flows through the ductus.

A small opening may not need treatment. A larger opening that is causing symptoms or other problems may be closed with surgery or a catheter procedure.