INTRODUCTION/OBJECTIVES: The primary objective was to compare the 24-h mean heart rate (HR) provided by a smart collar with 24-h ambulatory electrocardiography (Holter) in healthy dogs. The secondary objective was to compare the 2-min HR values between the two methods during periods of activity and rest. ANIMALS, MATERIALS, AND METHODS: Twelve healthy dogs were fitted with both Holter monitors and smart collars. Passing-Bablok regression and Bland-Altman (BA) agreement analysis were used to compare the 24-h mean HR between two methods. The BA analysis for repeated measures and bias plots were used to compare 2-min HR between methods. RESULTS: The regression analysis showed no significant differential or proportional bias between the methods to estimate 24-h mean HR. The BA analysis showed a mean bias of 2.2 beats per minute (bpm) (95% confidence interval = -0.2, 4.8) with an upper limit of agreement (LOA) of 9.6 bpm (5.1, 14.1) and a lower LOA of -5.1 bpm (-9.5 to -0.6). However, BA analysis of 2-min HR showed poor agreement between methods with wide LOAs at rest and during activity. The smart collar did not provide any HR information for 43% of the total possible recording duration (range = 24%-79%). STUDY LIMITATIONS AND CONCLUSIONS: The smart collar can provide a potentially clinically useful estimate of 24-h HR in dogs with normal sinus rhythm. The collar did not provide reliable 2-min HR measurements due to inaccuracies in HR estimation during periods of activity and the inability to report any HR during large periods of the recording.