Assessment of heart rate variability (HRV) is widely used in modern sports medicine to determine the functional state of the body, planning of training cycles and rehabilitation programs. This method is distinguished not only by its accessibility and versatility, but also by its high sensitivity to environmental conditions. In this article we decided to consider the possibility of using HRV parameters to assess the degree of body adaptation to heat stress. The article considers the impact of high temperature from the position of stress, gives a description of the basic mechanisms of adaptation and physiological processes under heat stress and considers the main works in which the impact of high temperature and HRV appears.