Where is the coronary sinus located and what does it do?

• A. Located near the floor of the left atrium and drains into the left atrium
• B. Located near the floor of the right atrium and drains blood from the myocardium into the right atrium
• C. Located on the posterior wall of the left ventricle and drains into the right ventricle
• D. Located along the interatrial septum and drains into the right atrium

Answer: (B)

The coronary sinus is the heart’s main venous drainage vessel, collecting most of the blood from the heart muscle and delivering it into the right atrium. It travels in the posterior portion of the coronary sulcus on the diaphragmatic (inferior) surface of the heart and opens into the right atrium near its lower region, close to the opening of the inferior vena cava. This placement explains why it is described as being near the floor of the right atrium, and it makes sense that its job is to drain deoxygenated blood from the myocardium into the right atrium. It does not drain into the left atrium or left ventricle, nor is it located along the interatrial septum, which is why the other descriptions don’t fit.