= Coronary artery
A \b[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.<Anatomy and Physiology 2e by J. Gordon Betts and others>[Section 19.1, Heart Anatomy, Coronary Circulation and Coronary Arteries; Figure 19.15]{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> is
$$
D_{\mathrm O_2}=QC_a.
$$
With chosen values $Q=250\,\mathrm{mL\,min^{-1}}$ and $C_a=0.20\,\mathrm{mL\ O_2\,mL^{-1}}$, delivery is $50\,\mathrm{mL\ O_2\,min^{-1}}$. If a representative venous oxygen content is $C_v=0.08\,\mathrm{mL\ O_2\,mL^{-1}}$, a steady-state inflow–outflow balance gives
$$
\dot V_{\mathrm O_2}=Q(C_a-C_v)=30\,\mathrm{mL\ O_2\,min^{-1}},\qquad
E=\frac{C_a-C_v}{C_a}=0.60.
$$
Here $E$ 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.<Nonoperative dilatation of coronary-artery stenosis: percutaneous transluminal coronary angioplasty by A. R. Grüntzig and others>[Abstract, paired stenosis and pressure observations]{ref} Neither observation by itself supplies all the information in the oxygen balance above.
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