= Anterior cardiac vein
An \b[<anterior cardiac vein>] drains part of the anterior <right ventricle> directly into the <right atrium>. This route bypasses the <coronary sinus>, unlike much of the other cardiac venous return.<Anatomy and Physiology 2e by J. Gordon Betts and others>[§19.1, Coronary Veins]{ref} The term anterior locates a drainage region; it does not mean an artery supplying that region.
The distinction matters to <coronary circulation> measurements. Collecting or sampling only the <coronary sinus> does not automatically collect this direct-return component. A vessel's endpoint is part of defining the experimental system, not just a label on an anatomical drawing.
An original simplified network contains a sinus route with flow $Q_s$ and an anterior direct route with flow $Q_a$, neglecting other routes. If their <venous oxygen contents> are $C_s$ and $C_a$, the combined coronary return has content
$$
C_{\mathrm{mix}}=\frac{Q_sC_s+Q_aC_a}{Q_s+Q_a}.
$$
For stipulated $Q_s=80$, $Q_a=20\,\mathrm{mL\,min^{-1}}$, $C_s=0.06$ and $C_a=0.10\,\mathrm{mL\ O_2\,mL^{-1}}$, the mixture is 0.068 in content units. Multiplying the sinus content by the full 100 mL/min would underestimate returning oxygen by $0.8\,\mathrm{mL\,min^{-1}}$.
The model does not assign normal flow fractions or cover every cardiac venous connection. It shows why an omitted return branch creates a transport error even if the sampled concentration is measured exactly. Following connected vessels in dissection or imaging tests the anatomical route; measuring flow and content tests the corresponding amount balance.
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