Abnormal persistence of an open lumen in the ductus arteriosus after birth, the direction of flow being from the aorta to the pulmonary artery, resulting in recirculation of arterial blood through the lungs.

Patent ductus arteriosus (PDA) is a medical condition in which the ductus arteriosus fails to close after birth: this allows a portion of oxygenated blood from the left heart to flow back to the lungs from the aorta, which has a higher blood pressure, to the pulmonary artery, which has a lower blood pressure. Symptoms are uncommon at birth and shortly thereafter, but later in the first year of life there is often the onset of an increased work of breathing and failure to gain weight at a normal rate...