Pulmonary atresia (uh-TREE-zhuh) is one of several heart valve defects that may be found at birth or soon after. In pulmonary atresia, the valve between the heart and lungs (pulmonary valve) is not fully developed, which prevents forward blood flow to the lungs, and your baby doesn't get needed oxygen.

Normally, some blood enters the lungs through other passages within the heart and its arteries. Before your baby is born, it receives blood through a hole (foramen ovale) between the top chambers of your baby's heart, and oxygen-rich blood is pumped out to the rest of your baby's body. After birth, the foramen ovale usually closes, but in pulmonary atresia it may stay open. Another temporary opening (ductus arteriosus) may allow some blood flow, but your baby will need medication, procedures or surgery to correct the atresia.

In this heart defect, there is also a hole between the two pumping chambers of your baby's heart (ventricular septal defect, or VSD). The pulmonary artery and its branches can be very small or nonexistent. In the latter case, additional arteries arise from the aorta to provide blood flow to the lung (major aortopulmonary collateral arteries, or MAPCAs).