This study investigates the benefits of weight loss on heart rate and spontaneous activity in 15 overweight dogs put on a 3-month weight loss program aimed to achieve a 1-1,5% weekly loss and fed with a diet with nutrients addressed to support heart function such as PUFA, taurine and L-carnitine. Mean body condition score went from 7 to 4.3. Body fat mass suffered a 60% reduction while lean body mass was preserved. Spontaneous activity increased by 1.5 and heart rate decreased a 17% at rest and during walks.