Not all fat is bad for your heart. Too much dietary fat is bad but the right kind of fat keeps the heart healthy, a promising study shows.Unsaturated dietary fatty acids such as eicosapentaenoic acid (EPA) are known to protect against cardiovascular diseases.In experiments over mice, Japanese scientists showed that mice engineered to produce their own EPA are protected against heart disease and have improved cardiac function.One particular EPA metabolite, called 18-hydroxyeicosapentaenoic acid (18-HEPE) was required for this protection.This was produced by immune cells called macrophages which dampened inflammation and fibrosis in the heart.Treatment with 18-HEPE confirmed its heart-protective effects."A diet enriched in 18-HEPE might thus help prevent heart failure in patients with cardiovascular diseases," noted researchers in a paper published in The Journal of Experimental Medicine.