<P> Approximately 70% of the general population are right - dominant, 20% are co-dominant, and 10% are left - dominant . A precise anatomic definition of dominance would be the artery which gives off supply to the AV node i.e. the AV nodal artery . Most of the time this is the right coronary artery . </P> <P> The papillary muscles attach the mitral valve (the valve between the left atrium and the left ventricle) and the tricuspid valve (the valve between the right atrium and the right ventricle) to the wall of the heart . If the papillary muscles are not functioning properly, the mitral valve may leak during contraction of the left ventricle . This causes some of the blood to travel "in reverse", from the left ventricle to the left atrium, instead of forward to the aorta and the rest of the body . This leaking of blood to the left atrium is known as mitral regurgitation . Similarly, the leaking of blood from the right ventricle through the tricuspid valve and into the right atrium can also occur, and this is described as tricuspid insufficiency or tricuspid regurgitation . </P> <P> The anterolateral papillary muscle more frequently receives two blood supplies: left anterior descending (LAD) artery and the left circumflex artery (LCX). It is therefore more frequently resistant to coronary ischemia (insufficiency of oxygen - rich blood). On the other hand, the posteromedial papillary muscle is usually supplied only by the PDA . This makes the posteromedial papillary muscle significantly more susceptible to ischemia . The clinical significance of this is that a myocardial infarction involving the PDA is more likely to cause mitral regurgitation . </P> <P> During contraction of the ventricular myocardium (systole), the subendocardial coronary vessels (the vessels that enter the myocardium) are compressed due to the high ventricular pressures . This compression results in momentary retrograde blood flow (i.e., blood flows backward toward the aorta) which further inhibits perfusion of myocardium during systole . However, the epicardial coronary vessels (the vessels that run along the outer surface of the heart) remain open . Because of this, blood flow in the subendocardium stops during ventricular contraction . As a result, most myocardial perfusion occurs during heart relaxation (diastole) when the subendocardial coronary vessels are open and under lower pressure . Flow never comes to zero in the right coronary artery, since the right ventricular pressure is less than the diastolic blood pressure . </P>

Which area of the heart receives its blood supply from the left circumflex artery