The superior vena cava enters superiorly and the inferior vena cava inferiorly and has a rudimentary valve. Medially, there is a small opening of the coronary sinus that drains venous blood from much of the heart waLl; this also has a rudimentary valve. The right atrium passes blood through the right atrioventricular (tricuspid) valves into the right ventricle.

The fossa ovalis forms a shallow depression in the interatrial wall. This indicates the position of the foramen ovale in the developing heart and its function (TO BE INSERTED).

The right atrium is divided vertically by the crista terminalis, a ridge on its lateral wall. Most of the atrial wall is smooth; it becomes ridged anterior to the crista terminalis by musculi pectinati, parallael muscle buncles running from the crista upwards towards the right auricle, a forward projection of the atrium around the base of the aorta.