Background: There is an assumption that the intensity of the control action of the autonomic nervous system (ANS) on a cardiac pacemaker is a function of the gradient of heart rate (HR), and is not proportional to it. The purpose of this study was to estimate the adequacy of the characteristics of the state of ANS according to the results of spectral analysis of cardiorhythmical characteristics and identify the general principles of the physiological interpretation of the results. Material and methods: Frequency spectrums of the dynamic series of changes of cardiac intervals for two groups of 78 Chinchila rabbits were studied: in the first group of animals were included rabbits with predominance of vagal mechanisms of regulation of heart rate (“vagotonics”), and in the second group – rabbits with a predominance of sympathetic mechanisms of regulation of heart rate (“sympathicotonics”). Results: It was shown that , under this approach, as the total power density spectrum (TP), and the total power in the high frequency (HF) and low-frequency (LF) regions of the spectrum from “vagotonics”, significantly higher than from “sympathicotonics”. However, if in “vagotonics” LF, on average, higher than HF, in “sympathicotonic” rabbits, conversely, HF higher than LF. It is reviewed the theoretical basis for the physiological interpretation of the results. Conclusions: It is suggested that if the high-frequency components of the spectral decomposition of changes of a cardiac intervals are adequate markers of vagal tone, the LF, likely characterizes the value, which is in a inverse proprtion to the degree of tension of the sympathetic division of the ANS at a given parasympathetic tone.