<P> The right coronary artery proceeds along the coronary sulcus and distributes blood to the right atrium, portions of both ventricles, and the heart conduction system . Normally, one or more marginal arteries arise from the right coronary artery inferior to the right atrium . The marginal arteries supply blood to the superficial portions of the right ventricle . On the posterior surface of the heart, the right coronary artery gives rise to the posterior interventricular artery, also known as the posterior descending artery . It runs along the posterior portion of the interventricular sulcus toward the apex of the heart, giving rise to branches that supply the interventricular septum and portions of both ventricles . </P> <P> There are some anastomoses between branches of the two coronary arteries . However the coronary arteries are functionally end arteries and so these meetings are referred to as potential anastamoses, which lack function, as opposed to true anastomoses like that in the palm of the hand . This is because blockage of one coronary artery generally results in death of the heart tissue due to lack of sufficient blood supply from the other branch . When two arteries or their branches join, the area of the myocardium receives dual blood supply . These junctions are called anastomoses . If one coronary artery is obstucted by an atheroma, the second artery is still able to supply oxygenated blood to the myocardium . However, this can only occur if the atheroma progresses slowly, giving the anastomoses a chance to proliferate . </P> <P> Under the most common configuration of coronary arteries, there are three areas of anastomoses . Small branches of the LAD (left anterior descending / anterior interventricular) branch of the left coronary join with branches of the posterior interventricular branch of the right coronary in the interventricular sulcus (groove). More superiorly, there is an anastomosis between the circumflex artery (a branch of the left coronary artery) and the right coronary artery in the atrioventricular groove . There is also an anastomosis between the septal branches of the two coronary arteries in the interventricular septum . The photograph shows area of heart supplied by the right and the left coronary arteries . </P> <P> The left and right coronary arteries occasionally arise by a common trunk, or their number may be increased to three; the additional branch being the posterior coronary artery (which is smaller in size). In rare cases, a person will have the third coronary artery run around the root of the aorta . </P>

Where does the venous blood from the coronary circulation enter the heart