An infant with patent ductus arteriosus is born with abnormal blood flow through the large vessels that deliver blood from the heart.

During development in the womb, the fetus receives oxygen from the mother's bloodstream. The developing fetus has a blood vessel, called the ductus arteriosus, which allows blood to bypass the fetal lungs. At birth, this blood vessel normally closes, allowing blood to flow to the lungs. In an infant with patent ductus arteriosus, the ductus arteriosus does not close properly at birth. Patent ductus arteriosus results in low blood oxygen levels and lung damage.

Ductus arteriosus may occur in premature infants, or in infants born with an abnormal heart.