Heart rate variability is a crucial physiological parameter that reflects the state of the autonomic nervous system and the organism’s level of adaptation to various conditions. In this study, an analysis of heart rate variability was performed in 30 clinically healthy male German Shepherd dogs aged 2 to 5 years, with body weight ranging from 28 to 38 kg. The study aimed to determine the features of heart rate variability in dogs with different autonomic tones (normotonia, vagotonia, and sympathicotonia) and to evaluate the relationships between heart rate variability parameters and physiological characteristics of the animals, such as age, body weight, and heart rate. The analysis was performed using Kubios HRV Scientific Lite software and methods of variational pulsometry. The results of the study demonstrated that in dogs with vagotonia, the electrocardiogram showed a significant prolongation of the mean duration of successive RR intervals, an increase in the standard deviation of all RR intervals, the root mean square of successive differences between the duration of adjacent RR intervals, the proportion of pairs of successive NN intervals, and a decrease in indices of autonomic balance and tension. These findings indicate a predominance of parasympathetic activity of the autonomic nervous system. In the group of sympathicotonic dogs, a decrease in the aforementioned parameters of heart rate variability was observed, along with a marked increase in the indices of autonomic balance and tension, indicating an elevated level of stress and a predominance of sympathetic activity. Normotonia was characterized by a stable balance between sympathetic and parasympathetic activity, as reflected in the average values of the main heart rate variability indices. The correlation analysis revealed strong associations between heart rate and the main parameters of heart rate variability. The influence of age and body weight on heart rate variability parameters was statistically insignificant, which confirms the predominance of physiological regulatory mechanisms. The results obtained highlight the importance of heart rate variability analysis for diagnosing the physiological state of dogs and assessing their adaptive capacity. Heart rate variability indices can be used as sensitive markers for monitoring stress, adaptive potential, and the risk of developing autonomic dysfunctions. Keywords: heart rate variability; autonomic nervous system; German Shepherd; vagotonia; sympathicotonia; autonomic regulation; pulsemetry.