Coronary sinus

The coronary sinus is formed by the continuation of the great cardiac vein in the coronary sulcus. As the great cardiac vein courses from the paraconal interventricular groove into the coronary groove, it enlarges and becomes the coronary sinus near the caudal aspect of the heart. Barone describe the coronary sinus as a vestige of the terminal segment of the left cranial vena cava (this vein being absent in carnivores and humans).

The coronary sinus ends in the right atrium with the opening of coronary sinus that is located into the caudal part of the right atrium, close to the interatrial septum and just dorsal to the opening of the caudal vena cava. The opening is a small, round to oval ostium. It is sometimes guarded by a thin, variably developed valve (valvula sinus coronarii, Thebesian valve in humans), which may be rudimentary or absent. This opening allows venous blood from the myocardium to drain directly into the right atrium.

In dogs, the coronary sinus is approximately 2 cm long and 5 to 8 mm in diameter. It lies in the epicardial fat of the dorsodextral part of the coronary groove ventral to the caudal vena cava and dorsal to the terminal part of the circumflex branch of the left coronary artery. It opens into the right atrium ventral to the termination of the caudal vena cava.