The influence of cardiac sympathetic nerve stimulation on certain aspects of ventricular excitation was examined in dogs at constant heart rate. Bipolar electrodes were used to record electrical activity from atrium, His bundle, right Purkinje papillary muscle junction, basal interventricular septum and the epicardial surface of the ventricles. Stimulation of the left stellate ganglion reduced markedly the A-V nodal delay, but produced little or no change of conduction velocity in the Purkinje system or in the pattern of epicardial depolarization. Conduction in muscle was enhanced slightly by stellate stimulation and appears to account for the observed decrease of 2 to 3 msec in ventricular activation time. These data indicate that cardiac sympathetic nerve stimulation does not result in major changes in the sequence of ventricular excitation.