The correct answer is: right atrium
The fossa ovalis is a depression in the right atrium of the heart. The fossa ovalis is a structure that retained from the fetal development. It is thin fibrous sheet that used to cover the foramen ovale. During the fetal development this structure was important for the blood transport from the right atrium to the left atrium, because of the nonfunctional fetal lungs . It closes immediately after the birth.
