Small cardiac vein

The 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.^[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.^[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.