Right atrioventricular orifice

The right atrioventricular orifice (ostium atrioventriculare dextrum) is the opening between the right atrium and right ventricle, guarded by the right atrioventricular (tricuspid) valve. It forms the anatomical and functional passage for blood flow from the right atrium to the right ventricle.

The right atrioventricular orifice is located at the junction of the right atrium and right ventricle, in the caudal part of the right atrium. It lies ventral to the opening of the coronary sinus (in species where distinct) and medial to the right auricle. Internally, it marks the transition from atrial myocardium to ventricular myocardium.

The orifice is generally oval to circular in shape. Its size varies according to species and body size. Its diameter changes slightly during the cardiac cycle due to contraction of surrounding myocardium.

The margin of the right atrioventricular orifice is reinforced by the right fibrous ring (part of the cardiac skeleton).