In the developing fetus, the<unk>  <unk>  is a shunt connecting the pulmonary artery to the aortic arch that allows most of the blood from the right ventricle to bypass the fetus' fluid-filled lungs. During fetal development, this shunt protects the lungs from being overworked and allows the right ventricle to strengthen.  There are two other fetal shunts, the ductus venosus and the foramen ovale.
Ductus arteriosus
Conus arteriosus
Atrioventricular canal
Interatrial septum
Aortic sinus
Tricuspid valve
Aorticopulmonary septum
Ductus venosus