Flavonoids are plant components of the diet. Their daily intake is about 1 g. In Poland the main source of flavonoids is tea, apples and onions. These compounds are characterized by a variety of biological activities and pharmacological effects. Especially important for human health are their antioxidant properties. This paper presents the current state of knowledge on the role and importance of flavonoids in the prevention of the initiation and development of cardiovascular diseases. Epidemiological observations, clinical research, in vitro and in vivo experimental studies clearly show a protective effect of flavonoids on the cardiovascular system. Their beneficial effects on the cardiovascular system involve the inhibition of low density lipoprotein (LDL) oxidation, the reduction of blood vessels permeability, antiplatelet and anti-inflammatory activity, and hypotensive and direct vasodilator action. Biological potential of flavonoids (especially the antioxidant activity) indicates the possibility of their use in primary and secondary prevention of atherosclerosis and its clinical consequences (heart attack, stroke, and others) as a safe potential therapeutic agents.