Small cardiac vein

The small cardiac vein (Right coronary vein) is a tributary of the coronary sinus that runs alongside the proximal-to-mid right coronary artery in the right atrioventricular groove and drains the inferior wall of the right ventricle. This vein is present in only 30-50% of individuals, making it a variable anatomic structure. When present, it typically measures less than 1 mm in diameter and rarely has an ostial valve.

The small cardiac vein demonstrates significant anatomic variability in its drainage pattern. In approximately 29% of individuals, it connects to the coronary sinus at the crux cordis (the junction of the atrioventricular and interventricular grooves). However, in many cases, it may drain independently into the right atrium rather than joining the coronary sinus. The small cardiac vein is considered a first-order tributary of the coronary venous system when it does connect to the coronary sinus.