 Coronary artery

A coronary artery is an artery supplying the heart's own tissues, especially the myocardium. The main left coronary artery and right coronary artery arise from the proximal aorta near the aortic valve. Their branches supply the working cardiac muscle rather than merely conveying blood through the heart's chambers.^[ref]

This arrangement separates two circulations that can otherwise be confused. Blood inside a cardiac chamber is being pumped onward; coronary blood flow brings oxygen and other materials to the living wall doing the pumping. An open chamber and a patent large coronary artery therefore answer different anatomical questions. Distribution through smaller vessels and exchange with tissue also matter.

An original conservation calculation illustrates the supply problem. If coronary volume flow is $Q$ and arterial oxygen content is $C_a$, then coronary oxygen delivery isWith chosen values $Q=250\mathrm{mL}\mathrm{mi}{\mathrm{n}}^{-1}$ and $C_a=0.20\mathrm{mL}{\mathrm{O}}_2\mathrm{m}{\mathrm{L}}^{-1}$, delivery is $50\mathrm{mL}{\mathrm{O}}_2\mathrm{mi}{\mathrm{n}}^{-1}$. If a representative venous oxygen content is $C_v=0.08\mathrm{mL}{\mathrm{O}}_2\mathrm{m}{\mathrm{L}}^{-1}$, a steady-state inflow–outflow balance givesHere $E$ is the coronary oxygen extraction fraction. The example assumes matched inflow and outflow from the same represented tissue, with negligible oxygen accumulation; these are illustrative values, not clinical reference limits. Delivery and extraction distinguish a flow measurement from the tissue's oxygen use.

Vascular stenosis can change the supply route, while the observed consequence depends on more than one geometric percentage. Coronary angioplasty targets a narrowed arterial segment. The historical primary study measured both stenosis and the pressure difference across the affected region, making anatomy and a physiological observation available together.^[ref] Neither observation by itself supplies all the information in the oxygen balance above.