Data concerning the age peculiarities of the heart rate characteristics of the children, especially of the school age, have important significance for the organism functional state evaluation. In this work during the investigation of the temporary structure of the cardiointervals number according to the common statistic indexes (medium length of the interval R-R, index of tension, mode amplitude, asymmetry, variation) the attractor dimension was estimated to evaluate the heart rate chaos level. The purpose of this work was the investigation of the age peculiarities of some indexes of the heart rate. During the investigation the age changes of the mentioned indexes were demonstrated and the attempts to explain the differences in the heart rate characteristics of the schoolchildren of different forms of the secondary schools were done.