Introduction and Objectives Holding determined body postures during work is connected with muscles activity. The more forced the posture, the larger the number of muscles taking an active part in holding and stabilizing the work posture. During logging, the greatest share of awkward (forced) working postures occurs in tree felling by chainsaw. Material and Methods A group of 10 experienced fellers aged 47.5±7.3 (37 – 59-years-old) was studied. Heart rate (HR) was measured during simulation of felling activity in 4 working postures: back bent forward with straight legs (stoop), back bent forward with bent legs (flexed-stoop), squat and kneeling on one knee (half-kneel). Results The lowest value of HR was noticed for squatting – 114.1 bpm, then for kneeling on one knee – 116.3 bpm. HR during felling in a standing posture with straight legs amounted to 121.5 bpm and for standing with bent legs 125.3 bpm. For all studied postures the differences in average HR values were statistically significant at p<0.01. Conclusions A working posture during tree felling by chainsaw has influence on the level of physiological workload of an operator. Standing bent forward body postures cause higher heart response than squatting and half-kneeling.