Smooth part of right atrium

The smooth part of the right atrium forms the posterior wall of the right atrium and is derived embryologically from the incorporation of the right horn of the sinus venosus. It is characterized by its smooth endocardial surface, in contrast to the anterior portion of the right atrium, which contains the right atrial appendage and is lined by pectinate muscles, giving it a trabeculated appearance.

The boundary between the smooth sinus venarum and the rough pectinated portion is marked internally by the crista terminalis.

This smooth region receives the openings of the superior and inferior vena cavae and the coronary sinus.