Blood supply to the heart begins at the aorta, immediately distal to the aortic valve in the sinuses of Valsalva.
The coronary arteries are 2-4 mm diameter vessels that are 5-10 cm long that run along the external surface of the heart.
The epicardial coronary arteries penetrate into the myocardium as intramural arteries that yield arterioles and capillaries in which nearly one vessel is adjacent to each cardiac muscle cell.
Three major epicardial coronary arteries are the left anterior descending (LAD), and the left circumflex arteries which arise from the bifurcation branches of the left main coronary artery, and the right coronary artery.
Branches of the left anterior descending coronary artery are the diagonal and the septal perforators and those of the left circumflex are the obtuse marginals.
Most blood flow to the myocardium occurs during ventricular diastole, when the coronary circulation is not compressed by the heart muscle.
With normal heart rate diastole contributes about 80% of coronary blood flow and about 20% occurs in systole.
Normal coronary artery blood flows in a laminar orientation and reaches its maximum velocity during diastole.
In the presence of tachycardia systole becomes a greater contributor to coronary artery blood flow.
The LAD artery supplies most of the apex of the heart, the anterior wall of the left ventricle and the anterior two thirds of the ventricular septum.
The artery that provides the posterior descending branch that perfuses the posterior third of the septum is the dominant artery and can arise from the right coronary artery or the left circumflex artery.
The left anterior descending artery and the left circumflex artery perfuse the majority of the left ventricular myocardium, with the LAD accounting for about 50% by itself.
A right dominant vasculature is present in 4/5th of individuals with the right coronary artery supplying the entire right ventricular free wall and the posterior basal wall of the left ventricle and the posterior third of the ventricular septum, while the circumflex branch of the left coronary artery perfuses the lateral wall of the left ventricle.
Occlusion of the right or left coronary artery can cause left ventricular damage.
Right and left coronary arteries are end vascular structures, but the heart has numerous intercoronary collaterals.
Arterial stenosis disrupts blood flow as it accelerates through a lesion and as flow velocity exceeds laminar thresholds turbulence occurs and produces an intracoronary murmur.
Intercoronary anastomotic vessels, the collateral circulation, is utilized when coronary artery vessels are narrowed, otherwise little blood flow through these vessels.
When coronary arteries are compromised and collateral circulation is inadequate the subendocardium tissues are the most vulnerable to ischemia.