Patent Ductus Arteriosus (PDA)Patent ductus arteriosus (PDA) is a condition in which the ductus arteriosus does not close. The word "patent" means open. The ductus arteriosus is a blood vessel that allows blood to go around the baby's lungs before birth. Soon after the infant is born and the lungs fill with air, the ductus arteriosus is no longer needed. It usually closes in a couple of days after birth. If the vessel doesn't close, it is referred to as a PDA. PDA leads to abnormal blood flow between the aorta and pulmonary artery, two major blood vessels that carry blood from the heart.