Fig. 2. Power spectra generated from heart beat interval data obtained from four rattlesnakes fitted with external miniature dataloggers, recorded for 110 h. For power spectral analysis ten individual data sets consisting of 512 consecutive RR intervals were chosen from each animal within each of the fH categories. The resultant power spectra within 0.001 Hz frequency bins were pooled to produce the plots. The standard error for the pooled data is not shown on the graph as it would mask components, but is instead expressed as more meaningful total powers for either low or high frequency components (see Table 2).