Many of the changes in cardiac performance that take place during exercise resemble those that result from stimulation of the sympathetic nervous pathways to the heart. It has therefore been thought likely that an increase in sympathetic nervous activity occurs during exercise and is important in the mediation of the associated cardiac response. To test this hypothesis a variety of experimental approaches have been employed. Sev- eral investigators have studied the manner in which surgical denervation of the heart in the dog affects its performance during exercise (1-7), and others have examined the effects of a variety of antiadrenergic drugs on the response to exercise in man (8-12). The results have been conflicting, with some groups ascribing little, if any, impor- tance to the sympathetic system in the over-all performance of the heart (1, 2, 4, 6, 7, 9-11), whereas others believe that the sympathetic nerves do play a major role (3, 5, 8).
Epstein et al. (1965) studied this question.