= Left marginal branch
The \b[left marginal branch] is a branch of the <circumflex artery> running toward the left ventricular margin and supplying part of the <left ventricle>. It belongs to the arterial supply of the <heart>'s tissue, rather than to the <blood flow> ejected from the ventricular cavity.<Anatomy and Physiology 2e by J. Gordon Betts and others>[§19.1, Coronary Circulation, Figure 19.15 and description of the circumflex marginal territory]{ref}
The parent connection is important: left identifies the relevant side, and marginal describes a course near a ventricular margin. A surface vessel in that region should not be identified solely by proximity. Tracing its origin from the <circumflex artery> distinguishes an arterial branch from a nearby <cardiac vein> and from branches of the <right coronary artery>.
Selective contrast injection provides an experimental way to examine such branching. A primary 1967 report described preformed catheters for selective <coronary angiography>, with serial or cine imaging in 100 consecutive patients.<Selective Coronary Arteriography: Part I: A Percutaneous Transfemoral Technic by Melvin P. Judkins>[Abstract, apparatus and patient series]{ref} The resulting image reveals a filled vascular route; it does not directly measure how much tissue oxygen was consumed along that route.
A simple branch balance illustrates the additional information needed. If total <blood flow> entering a segment of the <circumflex artery> is 100 mL/min and 30 mL/min enters one <left marginal branch>, the remaining downstream branches receive 70 mL/min in a no-storage model. The parent flow alone cannot determine the split. Vessel geometry, <vascular resistance> and the measurement location all affect what a branch-flow observation means.
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