Modifications of heart rate variability were investigated during intravenous-inhalation anesthesia in 80 cancer patients. Heart rate was recorded during active orthostatic test before surgical intervention as well as during: (1) before operation; (2) after atropine (0.01 mg/kg); (3) after intubation; (4) at the beginning of operation; (5) after 30 min from the beginning of operation; (6) after extubation. Heart rate power spectrum analysis with distribution to the three major oscillatory components was performed. Two groups of patients were investigated: (1) with normal baseline autonomic heart rate control and (2) with reduced one. During different stages of surgical intervention and anesthesia heart rate modifications in both groups were seen, although more expressed in patients with normal autonomic control. Concluding, heart rate variability changes throughout operation were related to different stages of anesthesia. Heart rate monitoring might be used for assessment of reflex and humoral heart rate control during anesthesia as well as for evaluation of operational stress.