The smallest cardiac veins or Thebesian veins or veins of Thebesius are minute valveless veins in the walls of all four heart chambers and they are often confused with the distinct set of arterial connections, the "vessels of Wearn". They are reportedly most abundant in the right atrium and least in the left ventricle. They drain the myocardium and pass through the endocardial layer to empty mostly into the right atrium, but a few empty into the ventricles. This is different from most cardiac veins, which normally empty into the cardiac sinus, which then empties into the right atrium. The openings of the chambers are called the foramina venarum minimarum.
The Thebesian venous network is considered an alternative (secondary) pathway of venous drainage of the myocardium.
^Snodgrass, Brett Thomas (1 July 2012). "Vessels Described by Thebesius and Pratt Are Distinct From Those Described by Vieussens and Wearn". The American Journal of Cardiology110 (1): 160. doi:10.1016/j.amjcard.2012.04.005. PMID22704295.