The end portion of the cardiac vein which empties into the right atrium. image
The left common cardinal (coronary sinus) lies in the body wall anteriorly, then crosses the septum transversum and enters the sinus venosus farther forward than the right common cardinal. The sinus enters the right atrium through the sinoatrial canal. The atrioventricular canal can be distinguished by the presence of the endocardial cushion.
The opening into the right atrium to which the veins of the left coronary circulation drain deoxygenated blood before it flows into the right atrium.
The coronary sinus is a vein that collects blood from the myocardium of the heart. It is present in humans and other animals.