[UPDATED] Latin words meaning "oval fossa" or "oval depression". The fossa ovalis is, as it names implies, an oval-shaped depression in the interatrial wall of the right ventricle. (see image, pointer "A"). The fossa ovalis represents in the adult the fetal communication between the right and left atrium allowing for fetal oxygenated blood to bypass the pulmonary circulation and enter the systemic circulation directly. The fossa ovalis is closed upon birth by two opposing membranes, and the higher pressure on the left side of the heart.

The persistence of the communication between the right and left atrium is known as an Atrial Septal Defect (ASD) and will need surgical correction. Some anatomists refer to this depression as the "foramen ovale" and it is surrounded by a well-defined muscular border known as the "limbus fossa ovalis", also known by the eponym "ring or anulus of Vieussens"

For more information: 

• On fetal circulation
• On the fossa ovalis (Gray's Anatomy)
• Image of the fossa ovalis (Gray's Anatomy)