The purpose of the research is to study and comparatively evaluate the changes in HRV indicators in functional tests of various directions. HRV was studied in 50 elite athletes (athletics, wrestling, judo, football) , at age 20-26 years old. The research was held in the scientific research laboratory of the Armenian State Institute of Physical Culture and Sport using the hardware - software complex "Varikard 2.5.1, Iskim - 6.2. The studies were carried out in the morning, in the preparatory phase of the training process, at rest and during functional testing. In orthotest HRV was recorded at rest 5 min supine followed by 5 min standing. 20 minutes later, a treadmill test was carried out on Treadmill Proteus LTD_7560 with a gradually increasing load (1 km/h per minute) until exhaustion. The duration of test was 13-15 minutes, HRV recorded after test 5 min supine. HRV time indicators - HR(b/m), MxDMn(ms), SI (un) and frequency (spectral) indicators - TP (ms2), HF (ms2), LF (ms2), VLF(ms2) are analyzed. The degree and direction of changes in HRV indicators are connected with the different type of stress factors, their intensity and duration. The HRV time indicators in both tests change unidirectionally: sympathetic activation causes an increase in heart rate, a decrease in the variation range MxDMn and an increase in the stress index SI, with the greatest degree of shifts in the treadmill test. The spectral indicators of HRV in both tests vary in different directions. In orthotest, the vasomotor center is activated, expressed by an increase in LF wave amplitude against the background of a decrease in the HF wave, but without a significant reaction from the total power of the TP spectrum and the humoral-metabolic component VLF. With the treadmill test, there is an energy-deficient state, expressed by a sharp decrease in TP wave amplitude and all spectral indicators reflecting the activity of individual management levels of heart rhythm control. The picture of correlation links emphasizes the balanced functioning of the autonomic nervous system at rest, increased sympathetic activity and regulation centralization in orthotest, as well as an imbalance of autonomic regulation in treadmill test.