Electrical stimulation of the carotid sinus nerve in the rabbit modifies the major components of cardiac performance. Serial determinations of cardiac output by the thermal dilution techniques indicated that cardiac output is moderately reduced (5%) under both thiopental and urethane anesthesia. No correlation was found between the reduction in blood pressure and the changes in cardiac output nor between the reduction in heart rate and the changes in cardiac output. Peripheral vascular resistance was constantly andsignificantly reduced (-24%). Cardiac work was also decreased (-33%).