We investigated the effects of omega- 3 fatty acids administration on endothelium- dependent vasodilation in patients< 65 years old who received treatment for chronic heart failure(CHF). Twenty patients(mean age 73 years; 15 men) with grade II and III CHF who were on maximal medical management were recruited. Patients were randomized in a double- blind, crossover fashion to 6 weeks of omega- 3 fatty acid(1.8 g ecosapentaenoic acid and 1.2 g docosahexaenoic acid) or olive oil. Forearm blood flow(FBF) responses to incremental doses of intra- arterial sodium nitroprusside, acetycholine(ACH), angiotensin- II, and Ng- nitro-l- arginine methyl ester were assessed by venous occlusion strain gauge plethysmography. The endothelium- dependent increase in FBF was greater in response in ACH infusion after omega- 3 fatty acid administration(7.9, 95% confidence interval [CI] 4.81 to 11.08 to 11.3, 95% CI 7.31 to 15.23 arbitrary units(p< 0.05) compared with baseline(7.95, 95% CI 4.8 to 11.08 arbitrary units) and olive oil administration(7.27, 95% CI 4.66 to 9.88 arbitrary units)(p=NS for both). Neither omega- 3 fatty acid nor olive oil altered endothelium- independent vasodilation in response to infusion of sodium nitroprusside, nor did they influence vasoconstrictor responses to angiotensin- II or Ng- nitro- l- arginine methyl ester. Dietary omega- 3 fatty acid supplementation was accompanied by an increase in FBF response to ACH, which represents enhanced endothelium- dependent vasodilation in CHF. Further studies are warranted to assess the mechanism responsible for the beneficial actions of omega- 3 fatty acids in CHF. We investigated the effects of omega-3 fatty acids administration on endothelium- dependent vasodilation in patients <65 years old who who received treatment for chronic heart failure (CHF). Twenty patients (mean age 73 years; 15 men) with grade II and III CHF Patients were randomized in a double-blind, crossover fashion to 6 weeks of omega-3 fatty acid (1.8 g ecosapentaenoic acid and 1.2 g docosahexaenoic acid) or olive oil. Forearm blood flow (FBF) responses to incremental doses of intra-arterial sodium nitroprusside, acetycholine (ACH), angiotensin-II, and Ng-nitro-l-arginine methyl ester were assessed by venous occlusion strain gauge plethysmography. The endothelium- dependent increase in FBF was greater in response (7.95, 95% confidence interval [CI] 4.81 to 11.08 to 11.3, 95% CI 7.31 to 15.23 arbitrary units (p <0.05) compared with baseline 11.08 arbitrar y units) and olive oil administration (7.27, 95% CI 4.66 to 9.88 arbitrary units) (p = NS for both). Neither omega- 3 fatty acid nor olive oil altered endothelium- independent vasodilation in response to infusion of sodium nitroprusside, nor did they influence vasoconstrictor responses to angiotensin-II or Ng-nitro-l-arginine methyl ester. Dietary omega-3 fatty acid supplementation was accompanied by an increase in FBF response to ACH, which represents enhanced endothelium- dependent vasodilation in CHF. Further studies are warranted to assess the mechanism responsible for the beneficial actions of omega- 3 fatty acids in CHF.