= Small cardiac vein
The \b[small cardiac vein] is a variable tributary of the <coronary sinus> that follows the right-sided coronary region, alongside part of the <right coronary artery>, and drains portions of the <right atrium> and <right ventricle>.<Anatomy and Physiology 2e by J. Gordon Betts and others>[§19.1, Coronary Veins]{ref}
The word small is part of an anatomical name, not a guarantee of a fixed diameter or of its presence in every specimen. In a dissection series of 37 adult human hearts, a <small cardiac vein> was identified in $54\%$ of specimens.<The anatomy of the coronary sinus and its tributaries by J. R. Ortale and others>[Abstract, small cardiac vein]{ref} That sample proportion describes the examined material; it should not be silently converted into a universal population frequency or a claim that the same tissue lacks drainage in other hearts.
A practical identification exercise begins at the <coronary sinus> and follows a candidate tributary toward the right-sided ventricular surface. Merely finding a narrow vessel is insufficient: the vessel's course and its connections establish the identification. Comparing the <small cardiac vein> with the <middle cardiac vein> is especially useful because the latter follows the <posterior interventricular sulcus>, a different landmark. The example shows why an anatomical route is a more reliable description than a name interpreted as a size threshold.
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