A patent ductus arteriosus (PDA) is a blood vessel, which connects the aorta to the pulmonary artery. This is normally present in the fetus and allows blood to bypass the lungs. The PDA usually closes within a few days in a full term infant. In premature infants, the closure may take longer.

When a PDA fails to close, "red blood" from the aorta mixes with "blue blood" in the pulmonary artery. This extra blood in the pulmonary artery travels to the lungs and left side of the heart. Over time, this extra blood may stress and damage the blood vessels in the lungs. In addition, the left side of the heart may enlarge as it works harder. A PDA may vary in size from small to large. Smaller PDA's will generally cause no symptoms or ill effects in the young child. A child with a large PDA might have poor growth and frequent respiratory infections. Surgical repair is recommended if the PDA remains open by three months of age. If the PDA causes significant problems, repair at a younger age may be required.

Children with PDA's require penicillin (also called SBE prophylaxis) prior to any dental work or surgery on the mouth, bowel, or bladder. This helps prevent the uncommon, but possible, occurrence of bacterial infection affecting the heart near the defect or heart valves.