The objective of this study was to quantify the intensity of different types of exercise by measuring heart rate and blood lactate level in sled dogs to better understand their aerobic capacities. Fourteen Alaskan huskies (seven males, seven females; age: 2.4 ± 0.4 years old; weight: 21.9 ± 0.9 kg) were involved in mild (45-minute walk on leash), moderate (2-hour trot at 8 mph), and intense (6- minute run at 22 mph) exercise. Heart rate and activity intensity were measured using Actiheart monitors (Mini-Mitter, Bend, OR) during the exercise, preexercise, and postexercise periods. Blood lactate was measured before and after exercise. Average heart rates during mild, moderate, and intense exercise were 159 ± 5.2, 179 ± 5.3, and 190 ± 2.7 bpm, respectively, and correlated with the increase in measured activity: 246 ± 15 counts/min (cpm), 454 ± 27 cpm, and 648 ± 27 cpm. Preexercise lactate values for mild, moderate, and intense exercise were 0.7 ± 0.1, 1.5 ± 0.2, and 1.3 ± 0.2 mmol, respectively. Postexercise lactate values were low after mild and moderate exercise (0.8 ± 0.1 and 0.7 ± 0.1 mmol) but higher after intense exercise (4.4 ± 0.7 mmol). By regression, we identified the lactate threshold as being around 2 mmol, corresponding to 74% maximum heart rate. Walking and trotting heart rates (64% ± 1.8% and 72% ± 2% maximum heart rate, respectively) were beneath the lactate threshold, indicating aerobic pathways as the main supply of energy. Onset of blood lactate accumulation (OBLA, 4 mmol) occurred at 76.5% maximum heart rate. Intense exercise (77% ± 1% maximum heart rate) was just beyond OBLA, indicating a large contribution from anaerobic metabolic pathways. The postexercise recovery times (time to recover preexercise heart rate) were equivalent after mild and moderate exercise but much higher after intense exercise (14 ± 2 and 15 ± 1 vs. 39 ± 2 minutes, respectively), reflecting the difference observed in postexercise lactate values and the theoretical higher oxygen debt after anaerobic intense exercise versus aerobic mild to moderate exercise. These results validate the use of Actiheart monitors in working dogs to evaluate the intensity of exercise. Together with blood lactate values, these monitors give a clear picture of the scope of these dogs’ aerobic capacity in response to different types of exercise.