Evidence from epidemiologic and clinical secondary prevention trials suggest that the omega-3 polyunsaturated fatty acids (n-3 PUFAs) may have a significant role in the prevention of coronary heart disease. Dietary sources of n-3 PUFAs include fish oils, rich in eicosapentaenoic acid and docosahexaenoic acid, along with plants rich in a-linolenic acid. Randomized secondary prevention clinical trials with fish oils (eicosapentaenoic acid, docosahexaenoic acid) and a-linolenic acid have demonstrated reductions in risk that compare favorably to those seen in landmark secondary prevention trials with lipid-lowering drugs. Several mechanisms explaining the cardioprotective effect of the n-3 PUFA have been suggested including antiarrhythmic and antithrombotic roles. Although official US guidelines for the dietary intake of n-3 PUFA are not available, several international guidelines have been published. Fish is an important source of the n-3 PUFA in the US diet; however, vegetable sources including grains and oils offer an alternative source for those who are unable to regularly consume fish.