INTRODUCTION Changing body position from supine to sitting results in heart rate (HR) response that may reflect complex pattern of the cardiovascular adaptive mechanisms. Testing of evoked changes in Heart Rate Variability (HRV) may provide important physiological information. AIM The study was performed to investigate HR-asymmetry (HRA) and entropy-based measures to compare heart rhythm complexity in stationary conditions in two body positions. METHODS 4 kHz-ECG was recorded (AdInstruments System, Australia) in two 15-min epochs, in supine and sitting position, in 40 healthy male students, aged 18 -20.Time series of 512 RR-intervals (RRi), were analyzed for HRA with use of dedicated software. Acceleration and decelerations runs and sequential monotonic changes of RRi interval were discriminated. Approximate entropy (ApEn) and sample entropy (SampEn) was computed with use of Kubios HRV Pro software (Finland). RESULTS In sitting position RRi were shorter (780 vs. 881 ms - supine), while ApEn and SampEn were lower (1.08 vs 1.23; 1.20 vs. 1.54). The ratio of the HR decelerations to accelerations (0.93 and 0.90 supine vs. sitting) correlated with ApEn (r =0.5237, r = 0,4581 supine vs. sitting) and SampEn (r = 0,3820 vs, r = 0,4900). In sitting position the number of monotonic RRi changes was decreased by 18,5%, what was mainly covered by a decreased runs of lenghts 2 (-52%). But the number of longer monotonic runs (lenghts 4 to 9) was significantly higher (up to +263%). The total number of short HR sequential runs (lenghts 2 to 3) was proportional to ApEn or SampEn (r > 0.64), whereas for longer runs (length 5 -8) the negative correlation (r < -0,51) was found. CONCLUSION HRA corresponds to the entropy based HRV measures. Nonlinear mechanisms related to the complexity of the heart rate control systems are involved in cardiac responses to changes in body position