Responses of the cardiovascular system to brief exposure to hypobaric hypoxia were the focus of this investigation. Impairment of adaptive reactions of the body was found to depend on the level of physical loading. "Critical" time of exposure to a simulated altitude of 5000 m came to 7-10 minutes. The deadaptive disorders have a non-specific character, e.g. hypotonia, dysrhythmias, etc. Probability of their emergence hinges on the physical state of subject. Low tolerance of chamber tests was a distinguishing feature of subjects with cardiovascular abnormalities.