The heart rate (h.r.) of normal healthy subjects varies in rest, under high-load conditions and in pathology. The heart rate variability (h.r.v.) integrates many mechanisms in- and outside the central nervous system, which influence and regulate the h.r. Statistical methods have been used to obtain additional information concerning the diagnostic capabilities h.r.v., the correlation between ECG R-R intervals and their variability and the prognostic significance of h.r.v. The benefits of modification of h.r.v. are not well known. In our previous study the h.r.v. of astronauts before, during and after long-term space flight (seven months) was examined. In this study we make analysis of h.r.v. in wake and sleep in different phases during a short-time space flight (9 days) of the Bulgarian astronaut A.A. in 1988.