Nitric oxide and its endogenous inhibitor Asymmetric dimethyl-l-arginine both are increased in the heart failure milieu and are related to pathophysiology of systolic impairment and endothelial dysfunction.Objective: To evaluate the levels of nitric oxide metabolites (NOx) (as indirect evidence of nitric oxide level) and the level of ADMA in patients with moderate to severe congestive heart failure; both ischemic and idiopathic etiologies , find any etiology-specific difference and test their relations to EF and endothelial function as measured by FMD. Methods: This was a case control study comparing cases of heart failure with normal control subjects. We studied serum levels of ADMA and NOx, echocardiographic parameters for LV dimensions and systolic function and the endothelial function by FMD. Results: We found that both ADMA and NOx were significantly elevated in sera of patients with heart failure compared to normal control [p <0.001 for both], there was an inverse correlation between EF and serum ADMA level [p = 0.008 , r = -0.403], EF and NOx [p = <0.001 , r = -0.943] A significant direct correlation was found between ADMA and NOx [p = <0.001 , r = 0.743]. There was no difference between ischemic and idiopathic groups in ADMA or NOx. Increasing age was directly correlated to ADMA [p = 0.002 , r = 0.470], to nitrites [p = 0.004 , r = 0.436] and to nitrates [p = <0.001 , r = 0.542], also endothelial function was worse in heart failure than in control subjects and inverse correlation was found between FMD and ADMA [p = 0.027 , r = -0.340] and between FMD and NOx [p = 0.011, r = -0.389]. However, neither of ADMA, NOx, EF nor FMD was proved to be correlated to NYHA FC. Conclusion: Increased NO in heart failure whether due to ischemic or idiopathic cardiomyopathy may be one of the mechanisms for systolic impairment and high ADMA level may explain endothelial dysfunction in heart failure although total NO production is increased.