Abstract
Of particular relevance today is the importance of heart rate variability. Heart rate - the force of contractions, regulated by the sympathetic and parasympathetic divisions of the autonomic nervous system, which is very sensitive to any stressful effects. Differences in clinical manifestations in children are explained by the heterogeneity of the child population, which manifests itself in variations in the strength of stress reactions - adaptation failure, in differences in the terms of "maturation" of functional systems. In children, depending on age, the polymodal nature of responsible reactions are clearly manifested: part shows hypersensitivity to them, part - complete anergy, stability or tolerance, and part meets the average reaction rate, an explanation for this existence of hereditary polymorphism in the human population.