The aim of the presents study is to make a comparison between heart rates measured at real altitude and at the simulated altitude (in hypoxic chamber), before and after the process of acclimatization. Six students (two women and four men) of Faculty of sport in Ljubljana participated in the study. They undergone eighteen day long acclimatization process on 2100 - 5642 m. Heart rates were measured in rest and during the step test before and after the acclimatization, at two locations: high altitude simulation chamber in Ljubljana and real altitude in Elbrus, Kavkaz, both at 2100 m. The results showed that heart rates were not significantly different between real altitude and simulated altitude. Acclimatization process caused a decrease of heart rates in both cases. From that we can conclude that it would be possible to train in hypoxic chamber and therefore shorten the acclimatization time in real very high mountains. Heart rate could be used as an objective parameter of the quality of the acclimatization. This should be proven in the future by research on bigger sample.