The effect of hypothermia and electrical stimulation of the perifornical caudal hypothalamus (PCH) on the autonomic nervous outflow to heart and arterial system was analyzed applying the discrete wavelet transform (DWT) to variability of the RR-interval and systolic arterial pressure (SAP). Rats were anaesthetized, under muscular blockade and artificially ventilated. Wavelet analysis of the cardiovascular response to PCH stimulation was done at core temperature (Tb) of 38ordm;C, during acute severe hypothermia from Tb 37ordm;C to Tb 25ordm;C and on rewarming to 38ordm;C. Core temperature was changed gradually, at a rate of 3ordm;C, every 15 min, using a thermostatted plate. Low (LF-sympathetic drive) and high (HF-parasympathetic drive) frequency components were obtained merging the details of signals with frequencies between 0.15-0.6Hz and 0.6-2Hz, respectively. Hypothermia induced a decrease of LF,HF and LF+HF from SAP signal that was not seen in heart rate (HR) analysis. No changes were observed for LF/HF in SAP and HR analysis, indicating a decrease of overall autonomic variability with no changes in net autonomic outflow. Hypothermia during PCH stimulation showed a significant increase of LF values without changes in HF. At the end of PCH stimulation a significant increase of HF was observed, indicating an increase of parasympathetic outflow to the heart better seen on HR signal. The effect of PCH stimulation on LF is reduced with cooling only in HR analysis. Rewarming restores autonomic outflow to control situations. Variability results indicate that cardiovascular changes of SAP and HR evoked on PCH stimulation follow different patterns of response.