= Left coronary artery
The \b[left coronary artery] is a principal <coronary artery> arising from the proximal <aorta>. Its typical major branches are the <left anterior descending artery> and the <circumflex artery>, which distribute blood to different regions of the <heart>.<Anatomy and Physiology 2e by J. Gordon Betts and others>[Section 19.1, Coronary Arteries and Figure 19.15]{ref} A main trunk and one of its branches are different anatomical levels; a finding in one should not be silently attributed to the other.
The adjective left does not partition the entire heart into two exclusive arterial territories. <Coronary dominance> and branching variations alter posterior supply, and a right-coronary system can supply substantial parts of the <left ventricle>. Injected-heart and X-ray observations demonstrate variation even within right-dominant specimens.<Functional dominance of the right coronary artery: incidence in the human heart by C. E. Nerantzis and others>[Abstract, variation within the right-dominant group and ventricular territories]{ref}
An original two-branch <conservation of mass> model makes the trunk-versus-branch distinction quantitative. If the modeled trunk has only two outlets and negligible accumulation,
$$
Q_{\rm left}=Q_{\rm anterior}+Q_{\rm circumflex}.
$$
Chosen branch flows $110$ and $70\,\mathrm{mL\,min^{-1}}$ give trunk flow $180\,\mathrm{mL\,min^{-1}}$. Measuring only the first branch would not supply the total. If other branches or alternate routes carry flow, their terms must be included rather than forced into this two-outlet model.
Likewise, the consequences of a narrowed main segment and a narrowed distal branch need not be interchangeable. They occupy different positions in a network. A physiological inference requires the actual routes, their resistances and the represented tissue, not merely the shared word coronary.
The <left coronary artery> is therefore a useful anatomical reference for interpreting <coronary angioplasty>, branch-level measurements and oxygen-supply models. A measured diameter identifies geometry at a selected location; <coronary oxygen delivery> additionally requires flow and <arterial oxygen content>. These observations must refer to compatible territories before they are combined.
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