Dr. Leaf former Chief of Medicine at Harvard Medical School wrote in the scientific journal Fundamental & Clinical Pharmacology “Any patient with an advanced state of impaired cardiac function should not be prescribed fish oil fatty acids or be urged to eat fish.” He told Dr. Dean Ornish "For these people, it may kill them."
So why is it that something that is beneficial to so many people may kill others? If you have congestive heart failure which is caused by a large amount of scar tissue on the heart muscle then your heart pumps just enough blood to keep you alive.
Omega-3's work to stabilize your heart by eliminating certain cells in order to maintain a steady rhytm. In the case of congestive heart failure it is possible that the Omega's will eliminate too many of the pumping cells resulting in death.
(Source: The Spectrum by Dean Ornish MD)
Remember supplements and vitamins are medicinal the same way that synthetic drugs are. Always consult a physician or naturopath about taking any supplement and inform your doctor of the vitamins and supplements you are taking.