Pulmonary artery
This is the remnant of the Botal duct (Latin ductus arteriosus (Botalli)), through which the fetus and blood entering the right ventricle are redirected from the pulmonary artery to the aorta: a small circle in the fetal stage of development does not function. In the future, the duct is obliterated (parallel overgrowth of the oval hole in the atrial septum).