Refers to the lack of formation of the heart valve between the right ventricle and the pulmonary artery. As there is no direct connection between the right ventricle and the pulmonary artery, the blood has to flow from the right to the left atrium via a hole in the atrial septum (foramen ovale) (right-left shunt), from there it enters the aorta mixed with oxygen-rich blood from the lungs and finally from there via the open connection of the ductus arteriosus into the pulmonary artery. Pulmonary atresia may be accompanied by a defect in the ventricular septum. As oxygen-poor and oxygen-rich blood mix, the newborns have cyanosis.
