Bottomline: An important study showing that high linoleic acid (omega-6 fat) stresses the heart.
Am J Physiol Heart Circ Physiol 293: H2919-H2927, 2007.

Summary. This animal study provides new evidence that 1 month of feeding a diet differing in the linoleic acid-to-alpha-linolenic acid (omega-6 to omega-3 fat ratio) has a dramatic effect on the heart cells.  When linoleic acid is high it  caused an increase in:
     -LOX and COX enzymes, central to activating the inflammation cascade in the heart
     -Arachidonic acid, the potent omega-6 fat, in heart cells
     -Enzymes that release fatty acids tethered to the phospholipids from heart cells
Notably, the different omega-6 diets tested reflect levels eaten by humans. The study demonstrated that the potential heart health benefits of high dietary ALA and  incorporation of EPA, and DHA is not achieved when the diet is rich in linoleic acid.   However, lowering the dietary omega-6 to omega-3 ratio closer to 1:1 decreases inflammatory enzymes activation and reduces lipid peroxidaton and nitrotyrosine production in the heart.

Study Quote: "Our results also clearly raise the possibility that any positive effects of ALA are only realized when the diet is also low in LA."

Comment: This is the first study to demonstrate a new way that excess dietary linoleic acid can hurt the heart---by inceasing nitrosative stress, which can damage heart tissue and DNA.  There have been two other studies on humans showing that high omega-6 fat diets can cause damage to the cardiovascular system (Eating Omega-6 Fat Hurts the Heart—Framingham Heart Study and Heart Disease and Clogged Arteries--Increased Risk with Dietary Omega-6 Fat_)


Link to Abstract:
Sanjoy Ghosh, Elizabeth M. Novak, and Sheila M. Innis.
Cardiac proinflammatory pathways are altered with different dietary n-6 linoleic to n-3 {alpha}-linolenic acid ratios in normal, fat-fed pigs. Am J Physiol Heart Circ Physiol 293: H2919-H2927, 2007.