n−3 polyunsaturated fatty acids (n−3 PUFAs) are essential for mammalian cells that are not able to synthesise de novo their precursor, α-linolenic acid, and may only partially convert it to eicosapentaenoic acid (EPA) and to a very small extent to docosahexaenoic acid (DHA). For this reason, nutritional guidelines for cardiovascular prevention recommend regular fish consumption (approximately two portions per week) in order to increase the intake of the n−3 PUFAs EPA and DHA, mainly referring to fatty fish, living in cold waters, usually very rich in these fatty acids. However, the indication to consume fish regularly is unlikely to be sufficient to ensure that patients with documented coronary heart diseases receive the daily amount of EPA + DHA (ca. 1 g) necessary for effective secondary prevention of the disease. This has prompted the development of pharmaceutical formulations both for dietary supplementation and for therapeutic administration, based on several dietary sources, containing greatly variable amounts of EPA and DHA, often with different availabilities. Critical knowledge of these characteristics allows the selection of the best approach in order to optimise the n−3 PUFAsupply in various individuals.