Coronary veins are blood vessels that drain deoxygenated blood from the heart muscle, or myocardium, back to the right atrium of the heart. They work in conjunction with the coronary arteries, which supply oxygen-rich blood to the heart. The main coronary veins include the great cardiac vein, middle cardiac vein, and small cardiac vein. These veins collect blood from the heart's surface and deeper layers, ensuring that waste products and carbon dioxide are efficiently removed. The coronary sinus is a large vein that collects blood from most of the coronary veins and empties it into the right atrium, completing the circulation process.