The study of the electrical activity of the sportsmen-swimmers' heart has been carried out during ventricular repolarization under short-term acute moderate normobaric hypoxia. It was revealed that acute hypoxia leads to a significant decrease of the duration of the early ventricular repolarization immediately after hypoxic exposure, of the duration of the late repolarization - at last minutes. The structural change of ventricular repolarization of the heart of the athletes surveyed was shown based on the changes in amplitude-temporal characteristics of the extrema of the heart electric field during the ventricular repolarization of the heart upon acute hypoxic exposure.