U-shaped patterns are acceleration-deceleration events characterized by high persistency of RR time intervals. Percentage contribution of U-shaped patterns to whole night-time series is small (in average 3%). However, the occurrence of U-shaped patterns affects to the properties of heart rate variability (HRV) significantly. The aim of this study is to evaluate its effect to nonlinear properties of HRV considering the ageing.Night-time 63 RR interval series from healthy subjects (26 males, 39 females, mean age: 40±14y) collected from the Institute of Cardiology and the Medical University of Gdańsk were analysed. Nonlinear properties of HRV were described by using DFA, Multiscale Multifractal Analysis (MMA) and Sample entropy.We found significant differences of Sample entropy (p20, 33 pts) number of U-shaped patterns. In turn, we observed significant difference of DFA α 1 between the patients =39y (33 pts) (p