Polyunsaturated fatty acids (PUFAs) include two series of fatty acids: omega-6 and omega-3 series. PUFAs have amphiphatic properties: hydrophilic head and hydrophobic tail. Such structure and other properties of unsaturated fatty acids are responsible for exerting the following biological action: maintaining cell-membrane fluidity, inhib- iting inflammatory processes, decreasing secretion of proinflammatory cytokines by monocytes/macrophages, decreasing susceptibility to ventricular rhythm disorders of the heart, improving functions of vascular endothe- lial cells, inhibiting blood platelet aggregation and decreasing triglyceride synthesis in the liver. In an organism, aracidonic acid (ARA) is converted to prostanoids series 2 (PGE2, PGI2, TXA2) and leukotrienes series 4 (LTB4, LTC4, LTD4) which are endowed with pro-inflammatory potential and are able to induce platelet aggregation and vasoconstriction. The metabolism of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) gives prostanoids series 3 (PGE3, PGI3, TXA3) and leukotrienes series 5 (LTB5, LTC5, LTD5); this group of eicosanoids shows anti-inflammatory, antiplatelet and antiarrhythmic properties.