Normally, a blood vessel needed only for fetal blood circulation (called the ductus arteriosus) closes off at birth. As the fetus develops, this blood vessel is kept open by a substance in the fetus's body called prostaglandin. At birth, prostaglandin decreases and the blood vessel closes.
In some premature infants, this blood vessel does not close. This is a condition called a patent (open) ductus arteriosus. These infants are given a prostaglandin inhibitor. It's a medicine to help the blood vessel close.
When an infant has certain other congenital heart defects, a medicine that is a form of prostaglandin is often given by vein to keep the ductus arteriosus open. Keeping this blood vessel open allows the blood to keep moving until the defect can be fixed to allow normal blood flow. This may require surgery or another procedure.