What happens to the foramen ovale after the baby's first breath?

• A. It closes and becomes the fossa ovalis
• B. It remains patent
• C. It enlarges to allow more flow
• D. It disappears

Answer: (A)

Postnatal circulatory changes cause the foramen ovale to close. When the baby takes the first breath, pulmonary resistance falls and blood flow to the lungs increases, raising left atrial pressure while right atrial pressure falls. This pressure shift pushes the flap of tissue (the septum primum) against the septum secundum, functionally sealing the opening and stopping the right-to-left shunt. Over time, fibrous tissue seals the hole, leaving a remnant called the fossa ovalis. In many people a small gap called a patent foramen ovale may persist, but the usual outcome is closure.