Stellate ganglion stimulation in the anesthetized, open-chest dog consistently resulted in the generation of pressure differences which averaged 20 mm Hg across the infundibular region of the right ventricle. Before stimulation, peak systolic pressures in the sinus and conus were closely matched. Peak sinus pressure showed ah average increase of 184 and 162% during stimulation of the left and right stellate ganglia, respectively. Simultaneously, peak conus pressure showed average increases of 88 and 61% during left and right stellate ganglion stimulation, respectively. In addition, the maximal rate of intrasinus pressure development (dP/dt) was usually elevated above conus dP/dt, and this change contributed to the generation of early systolic pressure differences. Cervical vagosympathetic nerve stimulation following atropine administration also resulted in the generation of infundibular pressure differences, but the latter were less marked than those elicited during stellate ganglion stimulation. Elevations in main pulmonary arterial resistance abolished the induced pressure differences by allowing peak conus pressure to rise to the same extent as peak intrasinus pressure. Simultaneous electromagnetic flow recordings of pulmonary arterial blood flow during stellate ganglion stimulation revealed two-to five-fold increases in maximum flow acceleration with relatively little change in stroke volume. Infundibular pressure gradients which developed in early systole were associated with maximum flow changes in the pulmonary artery.ADDITIONAL KEY WORDS stellate ganglion stimulation pulmonary arterial occlusion pulmonary arterial blood flow sinus and conus regions of the right ventricle vagosympathetic stimulation right ventricular infundibulum • The early anatomical and embryological studies of Sir Arthur Keith (1, 2) demonstrated that the conus arteriosus of the developing embryo was incorporated into the right ventricular myocardium and formed the terminal portion of the infundibulum in the adult heart. The conus homologue on the left side was obliterated during the embryological development of the left ventricle. In lower forms, From the Department of Physiology, Loyola University, Stritch School of Medicine and the Graduate School, 1400 South First Avenue, Hines, Illinois 60141.This work was supported in part by U. S. Public Health Service Grants HE 08682 and CM 999 from the National Institutes of Health.Received October 14, 1968. Accepted for publication, January 24, 1969. such as the tortoise, the conus arteriosus is anatomically distinct from the rest of the right ventricular musculature, and Woodbury and Robertson (3) demonstrated that this region can act as a functional stricture to divert blood through the interventricular foramen to the left ventricle. Studies on the canine heart by March et al. (4) have shown that the inflow or sinus region of the right ventricle is activated before the infundibular region, thus demonstrating physiological inflow-outflow pressure differences. Recently Tobin et al...