Increasing attention is being focused on the role of the autonomic nervous system in health and disease. The complex interplay between sympathetic and parasympathetic components establishes and maintains a dynamic adaptive state, permitting the organism to withstand innumerable perturbations and allowing both short- and long-term adjustments to the ever-changing environment. During rest and exercise, the autonomic nervous system mediates changes in arterial blood pressure, heart rate, and peripheral vascular tone to facilitate regional and systemic circulatory regulation. Recent investigations have been directed at improving our understanding of how the autonomic nervous system regulates exercise and recovery, as well as how the autonomic nervous system changes in response to long-term endurance training.

This article begins with a brief discussion of the measurement of autonomic function followed by a description of the autonomic dysfunction that occurs in cardiovascular disease and its prognostic significance. We then review the dynamic changes in autonomic function that occur during exercise and recovery from exercise. The effect of endurance training on resting heart rate, on the heart rate response to exercise, and on the pattern of heart rate recovery is then discussed with an emphasis on the autonomic mechanisms responsible for these changes. Finally, we discuss the beneficial effects of endurance training in patients with cardiovascular disease. Exercise training can be thought of as a therapeutic intervention that can restore healthy autonomic dynamics in patients with autonomic dysfunction. We conclude with some speculation on a potential mechanism by which exercise training may improve mortality in patients with cardiovascular disease and discuss the paradoxical observation that acute exercise confers increased risk of sudden cardiac death in susceptible individuals, while chronic exercise may be cardioprotective.