Editing Circulatory system (section)

====Coronary circulation====
{{Main|Coronary circulation}}
The heart itself is supplied with oxygen and nutrients through a small "loop" of the systemic circulation and derives very little from the blood contained within the four chambers.
The coronary circulation system provides a blood supply to the [[myocardium|heart muscle]] itself. The coronary circulation begins near the origin of the aorta by two [[coronary arteries]]: the [[right coronary artery]] and the [[left coronary artery]]. After nourishing the heart muscle, blood returns through the coronary veins into the [[coronary sinus]] and from this one into the right atrium. Backflow of blood through its opening during [[atrial systole]] is prevented by the [[Thebesian valve]]. The [[smallest cardiac veins]] drain directly into the heart chambers.<ref name="Guyton"/>