What is the central question of this study? We investigate whether NADPH oxidase activation mediates cardiac sympathetic nerve denervation and dysfunction in heart failure. What is the main findings and its importance? Cardiac sympathetic nerve terminal density and function were reduced in heart failure after myocardial infarction in rabbits. NADPH oxidase inhibitor apocynin prevents the reduction in cardiac sympathetic nerve terminal density and function in heart failure. These findings suggest that NADPH oxidase activation mediates cardiac sympathetic nerve terminal abnormalities in heart failure. NADPH oxidase may be a potential therapeutic target for cardiac sympathetic denervation and dysfunction in heart failure.Congestive heart failure (CHF) is characterized by cardiac sympathetic nerve terminal abnormalities, as evidenced by the decreases of norepinephrine transporter (NET) density and cardiac catecholaminergic and tyrosine hydroxylase (TH) profiles. These alterations are associated with increased reactive oxygen species (ROS). NADPH oxidase is a major source of ROS in CHF. In this study, we tested the hypothesis that NADPH oxidase activation mediates cardiac sympathetic nerve terminal abnormalities in CHF. CHF was produced by myocardial infarction (MI) in rabbits. Rabbits with MI or sham operation were randomized to orally receive an NADPH oxidase inhibitor apocynin (6 mg k g/day) or placebo for 30 days. MI rabbits exhibited left ventricular (LV) dilation and systolic dysfunction, and the increases in NADPH oxidase activity and 4-hydroxynonenal expression in the remote non-infarcted myocardium, all of which were prevented by the treatment of apocynin. Cardiac catecholaminergic histofluorescence profiles and immunostained TH and PGP9.5 expression were decreased, and the decreases were ameliorated by the apocynin treatment. NET, TH and PGP9.5 protein and mRNA expression were reduced and the reduction was mitigated by the apocynin treatment. The effects of apocynin were confirmed by utilizing the NADPH oxidase inhibitor diphenyleneiodonium in a separate experiment. In conclusion, the NADPH oxidase inhibitor apocynin attenuated increased myocardial oxidative stress and decreased cardiac sympathetic nerve terminals in CHF after MI in rabbits. These findings suggest that the activation of NADPH oxidase mediates cardiac sympathetic nerve terminal abnormalities in CHF, and the inhibition of NADPH oxidase may be beneficial for the treatment of heart failure.