The objective of this study was to evaluate the impact of weight loss on heart rate normalization at rest and during moderate exercise in overweight dogs. Spontaneous physical activity level evolution in relation with weight loss was also assessed. A group of 15 overweight dogs (average body condition score, BCS=7 on a 9-point scale) were enrolled in a 3-month energy restriction protocol to help them reach an ideal body condition. Weight loss rate was fixed at 1 to 1.5% of body weight loss per week for a steady and healthy weight loss. Dogs were fed a weight management diet enriched in key nutrients to support heart function (i.e., omega-3 fatty acids from fish oil, taurine and L-carnitine) and assigned to a daily walk of moderate intensity (5 km/h) for the 12-week study. At the completion of the study dogs recovered an ideal body condition (BCS=4.3). DEXA measurement showed maintenance of lean tissue and a 60% decrease in initial body fat mass. A normalization of lipid metabolism was observed with a significant decrease in blood triglycerides and an increase in circulating free fatty acids. Normalization of heart rate was also observed: heart rate decreased by 17% both at rest and during the walk after only 6 weeks on study, demonstrating a beneficial impact of both weight loss and exercise on heart function. Compared to initial levels, voluntary physical activity increased by 1.5 hours per day following weight loss. In conclusion, coupling a weight loss program together with daily standardized activity helped dogs recover an ideal body condition characterized by a better body composition with maintenance of lean tissues at the expense of fat. Blood parameters improved, while heart rate also normalized. This study highlights the fact that normalizing heart rate is a key parameter to take into consideration when treating overweight dogs in a weight loss program. Helping increase voluntary physical activity and promoting a better balance between energy input and energy expenditure will also be useful in preventing weight rebound.