In the epicardium of many mammals, animals, including humans, were found to have typical arteriovenular anastomoses. However, they do not correspond to the description of those direct anastomoses between arteries and veins located under the epicardium, which were previously identified. The authors who described them, using injection methods, showed the passage of carcass suspension from sub-epicardial arteries to sub-epicardial veins. But they could not accurately identify the type of vessels carrying out these connections. It is possible that these are arteriovenular anastomoses, since their diameter not exceeds the diameter of the blood capillaries. At the same time, it was shown that the vascular structures of the epicardium carry out the separation of the blood in the coronary artery system. As a result, blood with high hematocrit and freed from most various analytes and neutrophilic granulocytes enters the microvascular bed of the myocardium. The ultrafiltrate of the blood plasma in the sub-epicardial loose connective tissue undergoes biodegradation and is utilized in the lymphatic micro vessels. The aim of the work is the morphological and functional substantiation of the concept about of the epicardium as a biological filter of the heart. The vascular bed of the epicardium of hearts of mature dogs was studied (n=5), revealed by various routine histological and original intra- and extravascular methods. It is proved that the microvascular bloodstream of the sub-epicardial connective tissue has pronounced organ specificity. It is determined by the presence of arteriovenular anastomoses and permanent plasma capillaries, as well as the high permeability of all vascular components. The microvascular bed of the epicardium causes an ascending dilatation of the coronary arteries and contributes to ultrafiltration of a significant amount of blood plasma into the sub-epicardial interstitial space. Thus, the process of the separation of the blood is carried out, as a result of which blood with high hematocrit and free of neutrophilic granulocytes enters the myocardium. In the epicardial connective tissue, analytes accumulate that cannot be resorbed by venous micro vessels. This «biological debris» undergoes destruction in the sub-epicardial connective tissue, which proves the role of the epicardium as a biological filter of the heart.
