Heart rate variability (HRV) is related to vagal activity of the heart and can be used in the autonomic evaluation of the sinus node. In humans and horses it has been used to evaluate physical conditions, since HRV of athletes is associated with indicators of physical fitness, with the increase in vagal activity at rest. The aim of this study was the evaluation of the exercise (maximum stress test) on HRV in dogs of the Special Missions Battalion of the State Police of Espírito Santo (Brazil) in initiation of physical fitness. Nine dogs were used, five German Shepherds and four Belgian Malinois Shepherds, without distinction of sex, aged 20 months, and average weight of 25 kg. The dogs were submitted to electrocardiography in two stages: at rest (T0) and immediately after the progressive exercise test (T1), interrupted when the dog showed signs of exhaustion or when the exercise reached 20 minutes. The analysis of HRV was calculated in time domain through the analysis of 10 consecutive RR intervals (in milliseconds). The variables were analyzed for normality test by Shapiro-Wilk and for comparison by paired t-test considering p<0.05. Significant reduction was observed in HRV, with values of 14.92±0.22 at T0 and 14.47±0.36 at T1. This reinforces the good performance of the autonomic nervous system in controlling the sympathetic-vagal balance after physical activity of the evaluated dogs, being expected an overlap of the sympathetic nervous system on the parasympathetic with consequent reduction of the HRV.