Aim: To analyze changes in variational cardiointervalometry indicators in male rats that have undergone castration and stress and their combination. Materials and Methods: The research was carried out on 48 white sexually mature rats, aged from 1.5 to 3.0 months, weighing from 180 to 200 g. All animals were divided into 4 experimental group: 1 – control, 2 – gonadectomy, 3 – stress, 4 – gonadectomy and stress. To study heart rate variability, the method of variational cardiointervalometry was used on “Cardiolab” (Kharkiv, Ukraine). ECG analysis imclude calculation of heart rate (HR, min-1); variational range of cardiac intervals (.X, s); mode (Mo, s); amplitude of mode (AMo, %); tension index (TI); index of autonomic balance; autonomi. rhythm index; indicator of adequacy of regulatory processes. ECG recording was performed under thiopental sodium anesthesia. Results: Mo decreased in group 2 of rats, compared to 1, by 9.9 % (p<0.01). It was lower in group 3, compared to 1, by 11.2 % (p<0.001) and – group 4 – by 8.7 % (p<0.01). AMo decreased, compared to the control, only in group 3 by 22.4 % (p<0.001) and was lower compared to groups 2, and 4. The lowest .X values were observed in group 2 of rats. HR increased in group 2 of rats, compared to group 1, by 11.0 % (p<0.001), in group 3 of rats, compared to group 1, by 12.7 % (p<0.001) and was higher in this group, compared to group 4, by 8.0 % (p<0.01). Increase in the T. was noted in group 2 of rats, compared to group 1 of rats, by 2.5 times (p<0.001), in group 3 of rats, compared to group 1, – by 2.1 times (p<0.001), in group 4 of rats – by 88.7 % (p<0.001). Conclusions: A difference in the provision of autonomous regulation of heart rate was found in animals that had been stressed and castrated, which can cause the greatest damage to the heart with gonadectomy and stress.