Simultaneous measurements of pressure and flow have been made in the vessels of the aortic arch in chloralose-anesthetized dogs under three conditions; control, cardiac sympathetic (SS), and vagal nerve stimulation (VS). The specific sites studied include ascending aorta (AA), descending thoracic aorta (DTA), and brachiocephalic (BCA), left subclavian (LSC), and common carotid arteries (CA). Recorded data were analyzed by Fourier series methods and were used to calculate vascular impedance spectra, pressure and flow propagation characteristics, and hydraulic power. The distribution of cardiac output was found to be 70% to DTA, 22.2% to BCA, and 6.5% to LSC. The fraction of cardiac output to the BCA, LSC, and CA was increased by both SS and VS. The hydraulic power was distributed to the arch vessels nearly the same as the cardiac output. Hydraulic power dissipated in the arch vessels averaged 6% of the total AA hydraulic power and was increased by SS and decreased by VS. The results suggest that viscous losses in the arterial walls represent a considerable portion of the power dissipation. A similarity found in the vascular impedance spectra at the various sites for all three conditions was also observed for the transmission characteristics of pressure and flow harmonics between the sites. The results suggest that major reflections do not occur in the proximal aorta.