valve of the foramen ovale

This flap of tissue is called the valve of the foramen ovale.

The remains of the upper septum primum, will become the valves of the foramen ovale.

Consequently, the right atrium is generally under higher pressures than the left atrium, and the valve of the foramen ovale is normally open.

At birth, there is a reversal in the pressure gradient between the atria, resulting in functional closure of the valve of the foramen ovale.