Patent ductus arteriosus: Patent ductus arteriosus is a communication between the pulmonary artery and the aorta. This communication is normal present before birth (ductus arteriosus), but closes soon after birth. But if it remains patent, it leads to abnormal blood flow from the aorta to the pulmonary artery and the lungs. The extra blood returns from the lungs to the left atrium and then into the left ventricle. Patent ductus arteriosus overloads the left ventricle, which can fail in infancy.