Pulmonary atresia (uh-TREE-zhuh) is one of several heart valve defects that is found at birth or shortly afterward. In pulmonary atresia, the valve that allows blood to flow from the heart to the lungs (pulmonary valve) doesn't work correctly. Instead of opening and closing to allow blood to travel from the heart to the lungs, a sheet of tissue blocks blood flow.

Usually, some blood travels to the lungs through other passages within the heart and its arteries. Before birth, blood entering the right side of your baby's heart passes through a hole between the top chambers of your baby's heart (foramen ovale), so the oxygen-rich blood can be pumped out to the rest of your baby's body. After birth, the foramen ovale normally closes, but may stay open in pulmonary atresia. Another temporary opening (ductus arteriosus) may allow some blood flow to the lungs after birth, but your baby will need medication, procedures or surgery to correct the defect.