Wavelet analysis allows the evaluation of autonomic variability during short and non-stationary periods of time. In present work, heart rate (HR)(through the R-R interval) and systolic blood pressure (SAP) variability during the electrical stimulation of the hypothalamic defence area (HDA) of rats under different core temperatures has been analysed with wavelets Db 12 in order to evaluate the autonomic nervous outflow to heart and arterial system. Rats (n=8) were anaesthetised, under muscular blockade and artificially ventilated. During neuromuscular blockade, anaesthetic levels were assessed by observing the changes of arterial blood pressure and heart rate following a noxious stimulation by pinching a paw (for details see [1]). Wavelet analysis of the cardiovascular response to HDA stimulation was done during 3 conditions: 1) at core temperature(Tb) of 38C, 2) during acute severe hypothermia from Tb37C to Tb25C and 3)on re-warming to 38C (n=7). Core temperature was changed gradually, at a rate of 3C, every 15 min, using a thermostatic plate. Low (LF) -an indicator of the sympathetic drive- and high(HF) -related with parasympathetic outflow and respiration- frequency components were obtained merging the details of signals with frequencies between 0.15-0.6 Hz and 0.6-2 Hz, respectively. Hypothermia induced a decrease of LF, HF and LF+HF of SAP signal that was not seen on heart rate (HR) signal analysis. No changes were observed for LF/HF in SAP and HR, indicating a decrease of overall autonomic variability with no changes in net autonomic outflow. Hypothermia during HDA stimulation showed a significant increase of LF values without changes in HF. At the end of HDA stimulation a significant increase of HF was observed, suggesting an increase of parasympathetic outflow to the heart which was better seen on HR signal. The effect of HDA stimulation on LF is reduced with cooling only in HR analysis. Re-warming restores autonomic outflow to control situations. Results suggest that changes of blood pressure and HR evoked on HDA stimulation could follow different central pathways.