Cardioprotective action of omega-3 polyunsaturated fatty acids such as eicosapentaenoic and docosahexaenoic acid in fish and alpha-linolenic acid in plants was demonstrated in primary and secondary clinical trials. Fish oil therapy causes a marked decrease in serum triacylglycerol and very low density lipoprotein levels and increases moderately high density lipoprotein levels without any adverse effects. Omega-3 fatty acids decrease slightly, but significantly blood pressure, enhance endothelial function, they have anti-aggregator, anti-thrombotic and anti-inflammatory effects as well. These beneficial effects are in connection with modification of gene transcription levels of some key molecules such as nuclear factor-kappaB and sterol element binding receptor protein-1c, which regulate for example expression of adhesion molecules or several receptors involved in triglyceride synthesis (hepatocyte X receptor, hepatocyte nuclear factor 4alpha, farnesol X receptor, and peroxisome proliferator-activated receptors). On the basis of these observations, the supplementation of the diet with omega-3 fatty acids (fish, fish oil, linseed, and linseed oil or canola oil) is advisable in primary and secondary prevention.