<qa>  What is the prognostic significance of autonomic dysfunction?3. Autonomic dysfunction: Like heart failure, renal failure is characterised by autonomic dysfunction manifest by high resting sympathetic tone, impaired vagal control and reduced baroreflex sensitivity. The prognostic significance of autonomic dysfunction is not established for renal failure, but in chronic heart failure, the degree of dysfunction, measured by techniques such as heart rate variability, is a powerful and independent marker of prognosis. This evidence, coupled with the efficacy of beta-blocker therapy in heart failure, suggests that autonomic dysfunction can actively contribute to mortality and cardiovascular disease progression. Aldosterone appears to increase sympathetic and reduce cardiac vagal influence. The action of the sympathetic nervous system is increased as a result of reduced uptake of noradrenaline in the myocardium. A reduction in baroreflex sensitivity in response to aldosterone infusion has been demonstrated in both animals and man and in heart failure patients, an increase in heart rate variability occurred in response to aldosterone inhibition. We have recently shown that acute aldosterone receptor inhibition results in improved HRV markers of cardiac parasympathetic control in healthy subjects. 