oval foramen, 1. an opening in the septum between the right and the left atria in the fetal heart. This opening provides a bypass for blood that would otherwise flow to the fetal lungs. Most of the blood from the inferior vena cava in the fetus flows through the foramen ovale into the left atrium. After birth the foramen ovale functionally closes when the newborn takes the first breath and full circulation through the lungs begins. Also called foramen ovale. See also ductus arteriosus. 2. an oval foramen situated laterally to the foramen rotundum of the sphenoid bone.
