Rats are often used as animal models in experimental cardiology for studying myocardial infarctions and various cardiologic procedures. Currently the cardiac venous system is a target for the delivery of drugs, gene vectors, angiogenetic growth factors, stem cells, and cardioprotective reagents. The purpose of this study was to describe the anatomic configuration and variability of the cardiac venous system in Wistar rats, by using the corrosion cast method and perfusion of colored latex. The distribution of veins in the rat heart disagrees with prior descriptions for other mammals, except mice, which have a similar pattern. Coronary venous drainage in the 36 rats examined consistently involved the left cardiac, left conal, major caudal, right cardiac, and right conal veins. Other veins involved inconsistently included the cranial cardiac vein (58.3% of cases), minor caudal veins (16.7%), conoanastomotic vein (66.7%), and left atrial vein (75%). In 4 cases (11.1%), the collateral veins were located between the left conal and left cardiac veins. In this study, high morphologic variability between cases was manifested by differences in the arrangement, size, mode of opening, and formation of the common root and affected all regions of the heart but primarily the right ventricle.