Abstract Sleep is characterized by periods of cortical and subcortical desynchronization similar to that observed during arousal. Because baroreflex control of heart rate is suppressed in the aroused state, the present study compared the cardiac index of baroreflex sensitivity in awake cats with that during desynchronized sleep to determine the level of arousal and its affect on autonomic regulation. Cats were prepared for long-term arterial pressure, cortical, and subcortical EEG and EMG recording. After acclimatization to the laboratory, cats engaged in spontaneous periods of desynchronized sleep. During this period, a bolus of angiotensin II was injected i.v. and the subsequent change in the R-R interval of the cardiac cycle was recorded during the rising phase of the pressor response. These values were compared with values obtained from the same cats during quiet and active wakefulness and those obtained during drug-induced desynchronized sleep with gamma-hydroxybutyrate. The values obtained during naturally occurring desynchronized sleep were comparable to those observed during drug-induced desynchronized sleep. In contrast, the increase in the R-R interval in awake cats, particularly quiet ones, was greater than that seen during desynchronized sleep or during active periods in the awake animal. These data suggest that there is a correlation between the level of arousal, as measured by EEG activity, and the cardiomotor component of baroreflexes.