Abstract <p>It is well known that astronauts are exposed to stress during space flight (SF). One potential problem associated with SF is disruption of the bioelectrical conductivity characteristics of the heart muscle, manifested as arrhythmias. The article analyzes the results of a study of changes in heart rate variability study in a group of 5 astronauts (age 46 ± 4.5 years), in whose ECG records arrhythmias of atrial and/or ventricular origin were found. The average duration of the regular flight program of each astronaut was about 6 months. An analysis of experimental data on the prevalence of cardiac arrhythmias may indicate the arrhythmogenicity of SF. It was shown that the incidence of ventricular extrasystoles during SF increases compared to their incidence before SF. The incidence of atrial extrasystoles increases toward the end of spaceflight. The greatest number of cases of extrasystole was recorded after work in outer space. The planned construction of the Russian orbital (service) station—RO(S)S will increase the number of spacewalks by astronauts, and this must be taken into account, since the additional load on the cardiovascular system during extra-ship activities can contribute to heart rhythm disturbance.</p>