Final answer:
The coronary sinus drains into the right atrium, where it joins blood from the superior and inferior venae cavae before being transferred to the right ventricle and sent to the lungs for oxygenation.
Step-by-step explanation:
The coronary sinus empties into the right atrium of the heart. This is where most of the coronary veins that return systemic blood from the heart muscle itself drain into. It is located slightly superior and medial to the opening of the inferior vena cava on the posterior surface of the right atrium. The right atrium serves as the receiving chamber for blood coming back to the heart from the systemic circuit, including the blood that has flowed through the heart's own vascular system.
The two major systemic veins, the superior and inferior venae cavae, alongside the coronary sinus, lead deoxygenated blood back to the right atrium. The superior vena cava drains blood from regions above the diaphragm, such as the head, neck, and upper limbs, while the inferior vena cava carries blood from below the diaphragm, including the lower limbs and abdominal regions. This efficient system ensures that all the systemic venous return reaches the right atrium, which then transfers blood into the right ventricle to be pumped to the lungs for oxygenation.