The goal of this study was to evaluate the changes in blood pressure (BP) and heart rate variability (HRV) parameters due to a mental load. The findings indicate that mental arithmetic stress causes prompt increases in BP, heart rate and induced decreases in HRV. A shift toward an increase in sympathetic tone and changes in Poincare plot measures were observed during mental stress. The present study demonstrates that mental stress leads to an increase in predictability, regularity of the RR intervals and decreased value of complexity measures, that reflects a change towards more stable and periodic behavior of the heart rate under stress. Linear Discriminant Analysis shows that CCM and SampEn achieving the best results in detecting stress condition, and the latter indicates that chaos being inherent to the physiological control of heart rate.