= Coronary circulation
The \b[<coronary circulation>] supplies and drains the <heart>'s own tissue. <Coronary arteries> branch from the <aorta> to supply the <myocardium>; <cardiac veins> return blood toward the <right atrium>.<How Blood Flows through the Heart by NHLBI>[Supplying oxygen to the heart's muscle]{ref} Blood moving through a ventricular cavity is not the same flow as blood perfusing the surrounding muscle.
Much coronary venous return passes through the <coronary sinus>, while <anterior cardiac veins> provide a direct route to the <right atrium>.<Anatomy and Physiology 2e by J. Gordon Betts and others>[§19.1, Coronary Veins]{ref} Consequently a coronary-sinus sample represents its drainage territory rather than automatically every part of the heart. Anatomical pathways must match the region whose <blood flow> and oxygen uptake are being estimated.
An original tissue-balance example uses regional flow $Q=80\,\mathrm{mL\,min^{-1}}$, <arterial oxygen content> $C_a=0.20\,\mathrm{mL\ O_2\,mL^{-1}}$ and matching <venous oxygen content> $C_v=0.08$ in the same units. Then regional <coronary oxygen uptake> is
$$
\dot V_{\mathrm O_2}=Q(C_a-C_v)=9.6\,\mathrm{mL\ O_2\,min^{-1}}.
$$
The arterial delivery rate is $QC_a=16$ in those units. Delivery and uptake differ because oxygen remains in the returning blood. The values are stipulated, not normal-reference limits.
A primary 2007 experiment measured coronary volumetric flow using continuous saline <thermodilution>, an infusion <catheter> and a pressure/temperature guidewire, with comparisons in dogs and patients.<Direct volumetric blood flow measurement in coronary arteries by thermodilution by Wilbert Aarnoudse and others>[Abstract, Methods]{ref} This provides a concrete way to investigate the flow term; it does not by itself measure the oxygen-content difference.
The arterial map also varies among hearts. A radiopaque-injection study classified 178 of 200 examined hearts as right dominant by the origin of the posterior interventricular artery.<Functional dominance of the right coronary artery: incidence in the human heart by C. E. Nerantzis and others>[Abstract]{ref} Dominance names an anatomical branching criterion, not a claim that one artery supplies the entire heart.
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