Regulation of the cardiac chronotropic function was studied by spectral analysis of cardiac rhythm variability in HF, LF, and VLF bands in rats at various stages of the early postnatal ontogeny. The inadequacy of the regulatory mechanisms during the first days of life manifested by low power of all waves (particularly HF) in the cardiac rhythm variability spectrum. On day 14 of life, the cardiointerval variability was formed by HF waves, their low power together with increasing heart rate indicating more intense sympathetic effects. On day 21 of life, a potent elevation of the VLF power reflected a stronger centralization of regulation from higher autonomic centers. The age of 28 days was characterized by a sharp increase of HF activity and could be regarded as the turning point in the development of parasympathetic effects and activity of the autonomic regulation contour. From the age of 35 days, the wave power and the proportion of the spectral components of cardiac rhythm variability in albino rats corresponded to the adult pattern; a trend to the central regulation predominance and to greater rigidity of cardiac rhythm formed only with the onset of sexual maturation.