The article describes the results of studies of the reactions of the cardiovascular system to hypoxia, emerging in simulated dive, in adapted to the water athletes (divers, free divers, synchronized swimming sportswomen) and in not adapted subjects. It is shown that in adapting to breath hold during immersion in water in athletes compared with not adapted subjects protective cardiovascular reactions characterize by: reducing the degree of slowing of heart rate, constriction of peripheral vascular moderately pronounced, changing in cerebral bloodflow are more identified at the level of resistive vessels in the basin of the carotid arteries (the frontal-mastoid site of registration).