To evaluate the effect of total artificial heart replacement on the autonomic nervous system, sympathetic neurograms were analyzed by power spectrum and coherence function. Two pneumatically driven, sac type ventricular assist devices were implanted as biventricular bypasses (BVB) in adult, mongrel dogs. After initiation of BVB pumping, the natural heart was electrically fibrillated to form a BVB TAH model. Renal sympathetic nerve activity (RSNA) was recorded using a bipolar electrode attached to the left renal sympathetic nerve. RSNA was amplified and integrated by use of an R-C integrator. Power spectra of the RSNA and values of squared coherence between the arterial pressure wave form and the RSNA were calculated by computer. In animals with total artificial hearts (TAHs), coherence at the cardiac rhythm frequency was decreased, and coherence at the TAH pumping rhythm frequency was increased. These results indicate that the arterial pulse wave observed in TAH animals contributed to the sympathetic neurogram.