The aim of this study was to determine a heart rate deflection point (HRdp) in competitive agility dogs. Fourteen healthy border collies underwent progressive incremental treadmill exercise--modified Conconi test protocol. Heart rate was continuously recorded, and the HRdp was estimated using two methods: subjective and computer aided regression. Maximal heart rate (HRmax), achieved running speed at the anaerobic threshold and at the end of test were also determined. Statistical analysis showed a very high positive correlation between HRdp determined by two methods. The mean HRdp in this research corresponded to 80% of HRmax. The wide range of individual HRdp (162-229 BPM) indicates the need of an individual approach in assessing physiological parameters. To the authors' knowledge, this is the first application of Conconi modified test for estimating anaerobic threshold in agility dogs since the standard for dogs is yet undetermined. Future studies need to detect the most appropriate and reliable technique for its determination as well as its applicability in programming of the optimal training intensity.