No pulmonary valve exists, so blood can't flow from the right ventricle into the pulmonary artery and on to the lungs. The right ventricle acts as a blind pouch that may stay small and not well developed. The tricuspid valve is often poorly developed, too.

An opening in the atrial septum lets blood exit the right atrium, so venous (bluish) blood mixes with the oxygen-rich (red) blood in the left atrium. The left ventricle pumps this mixture of oxygen-poor blood into the aorta and out to the body. The baby appears blue (cyanotic) because there's less oxygen in the blood circulating through the arteries. The only source of lung blood flow is the patent ductus arteriosus (PDA), an open passageway between the pulmonary artery and the aorta. If the PDA narrows or closes, the lung blood flow is reduced to critically low levels. This can cause very severe cyanosis.

Early treatment often includes using a drug to keep the PDA from closing. A surgeon can create a shunt between the aorta and the pulmonary artery to help increase blood flow to the lungs. A more complete repair depends on the size of the pulmonary artery and right ventricle. If the pulmonary artery and right ventricle are very small, it may not be possible to correct the defect with surgery. In cases where the pulmonary artery and right ventricle are more normal size, open-heart surgery may produce a good improvement in how the heart works.

If the right ventricle stays too small to be a good pumping chamber, then the surgeon can connect the right atrium directly to the pulmonary artery. The atrial defect also can be closed to relieve the cyanosis. This is called a Fontan procedure. Children with pulmonary atresia require lifelong follow-up by a pediatric cardiologist.

People with pulmonary atresia, before and after treatment, are at risk for getting an infection on the heart's walls or valves (endocarditis) . To help prevent this, they'll need to take antibiotics before certain dental and surgical procedures.