What is limbus fossa ovalis?

Limbus fossa ovalis (also known as the limbus of fossa ovalis or the annulus ovalis) is a small, oval-shaped depression located in the right atrium of the heart. It is a remnant of the foramen ovale, which is the opening between the two atria that allows fetal blood to bypass the non-functioning lungs during gestation.

In approximately 75% of adults, the foramen ovale closes shortly after birth, creating the limbus fossa ovalis. The remaining 25% of individuals have a patent foramen ovale, which means the opening between the atria remains open. This condition is usually asymptomatic but may lead to complications such as stroke or migraine in some cases.

The limbus fossa ovalis is a useful anatomical landmark for performing invasive cardiac procedures such as cardiac ablation or transseptal puncture. It is also used as a reference point for different cardiovascular measurements.