Osmosis video - Patent ductus arteriosus

Patent ductus arteriosus (PDA) is a congenital heart defect in which the ductus arteriosus, a blood vessel that normally closes after birth, remains open. During fetal development, the ductus arteriosus connects and shunts blood from the pulmonary artery to the aorta, because the fetus doesn't use its lungs yet.

Initially, PDA causes a left-to-right shunt, resulting in pulmonary hypertension. Over time, as the pulmonary artery pressure increases, this is converted into a right-to-left shunt. This switch in the shunt is known as Eisenmenger's syndrome. PDA can be treated with the drug indomethacin, or by surgical ligation.