When the foramen ovale closes immediately after birth, what does it become?

• A. Fossa ovalis
• B. Ligamentum arteriosum
• C. Interatrial septum
• D. Foramen ovale

Answer: (A)

When birth shifts blood flow and pressure, the flap that covers the opening between the atria seals off, so the foramen ovale closes. The opening itself doesn’t stay open; it leaves behind a fibrous remnant in the wall between the atria called the fossa ovalis. The rim around it is known as the limbus fossae ovalis. This is why the correct description of what the foramen ovale becomes after birth is the fossa ovalis. For context, the ligamentum arteriosum would be the remnant of the ductus arteriosus, not the foramen ovale, and the interatrial septum remains the structure that encloses this area.