The invention relates to organic chemistry area and more particularly to the polyunsaturated fatty acids area. The invention specifically relates to nutraceutical or pharmaceutical compositions rich in unsaturated fatty acids, characterized in that they contain free or combined .alpha.-linolenic acid, associated with fatty acids having five and six double-bonds, admixed with a diluent or vehicle suitable for oral administration. These compositions are used for preventing or treating human or animal cardio-vascular diseases, at a dose ranging from 800 to 1,000 mg of .alpha.-linolenic acid, from 80 to 120 mg of eicosapentaenoic acid and from 800 to 1,000 mg of docosahexaenoic acid.