Nobody really knows whether fish oil supplements prevent heart attacts as effectively as eating fish. However, both eating fish and taking fish oil pills can lower triglycerides and prevent clotting, which may help prevent heart attacks. Heart attacks occur when a plaque breaks off from the wall of arteries leading to the heart and travels down the ever-narrowing artery until it stops and forms a clot that blocks blood flow to the heart.
A recent report shows that nine grams of fish oil supplements per day may not be completely safe because they can cause a substantial rise in the bad LDL cholesterol (from 106 to 186) that increases heart attack risk ( The Annals of Pharmacotherapy , July 2007). Fish oil supplements lower triglycerides by reducing liver cells' ability to manufacture triglycerides. At the same time, they can block the LDL receptors on liver cells from removing LDL from the bloodstream. Once again, I recommend getting the nutrients your body needs from food rather than from supplements. Diet to lower cholesterol ; how to raise the good HDL cholesterol