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Objectives: It was our aim to study the levels of L-arginine, the substrate for nitric oxide and asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, and their relation to the maintenance of sinus rhythm after electrical cardioversion for atrial fibrillation (AF), as well as the effects of angiotensin receptor blockade on these variables., Methods: In a double-blind, placebo-controlled study, patients with persistent AF were randomised to receive candesartan 8 mg once daily or placebo for 3-6 weeks before and candesartan 16 mg once daily or placebo for 6 months after cardioversion. As part of this study, plasma levels of L-arginine and ADMA were measured at baseline and at the end of the study., Results: Baseline levels of L-arginine, ADMA and the L-arginine/ADMA ratio were not predictive of rhythm outcome, and their levels were not influenced by treatment with candesartan. However, the L-arginine/ADMA ratio increased in patients who remained in sinus rhythm (n = 37) for 6 months when compared with patients with AF recurrence (n = 61; p = 0.008)., Conclusion: Neither L-arginine nor ADMA or their ratio were predictive of rhythm outcome after cardioversion, and they were not influenced by treatment with candesartan. However, the L-arginine/ADMA ratio increased in patients still in sinus rhythm 6 months after cardioversion., (Copyright © 2010 S. Karger AG, Basel.)