Final answer:
The foramen ovale is an opening in the interatrial septum that allows blood to flow from the right atrium to the left atrium and closes after birth.
Step-by-step explanation:
The foramen ovale is an opening in the interatrial septum that allows blood to flow from the right atrium to the left atrium. A valve associated with this opening prevents backflow of blood during the fetal period. As the newborn begins to breathe and blood pressure in the atria increases, this shunt closes. The fossa ovalis remains in the interatrial septum after birth, marking the location of the former foramen ovale.