Pulmonary atresia means that there is no connection between the right ventricle and the pulmonary artery, which prevents blood from flowing out of the right ventricle and to the lungs. Instead, blood is forced through a hole (an atrial septal defect) between the top two chambers (atria) to send deoxygenated blood to the left side of the heart. The deoxygenated blood travels through the aorta and ductus arteriosus (a connection between the aorta and pulmonary artery) to reach the pulmonary artery and lungs. The right ventricle is often underdeveloped and very small (hypoplastic). Babies born with this condition need a way for the de-oxygenated blood to reach the lungs and pick up oxygen.