GLOSSARY

The interatrial septum is the thin musculofibrous wall that separates the right atrium from the left atrium.

Characteristics

• Fossa ovalis: a depression on the right side of the septum, the remnant of the fetal foramen ovale.
• Fetal role: in the fetus, because the lungs are not functioning, most blood passes directly from the right to the left atrium through the foramen ovale, bypassing the lungs.
• Closure after birth: when breathing begins and left atrial pressure rises, the flap of the foramen ovale closes and usually fuses over the following months.

Clinical Application