The allometric relationship between body weight and heart rate (HR) has been described during the years as inversely proportional between the domestic species, being higher in species such as small rodents and lower in whales. Based on these principles, the normal range of heart rate in dogs, according to several references, has been described according to the size and body weight. However, the relationship between body weight and heart rate in dogs (small breeds - higher HR; large breeds - smaller HR) that has been proposed for decades is currently being refuted. The aim of this study was to investigate the relationship between HR and body weight in healthy dogs, as well as the influence of weight on clinical parameters and electrocardiographic variables. One-thousand electrocardiographic tracings (575 females and 425 males) were analyzed, and animals were divided into five body weight groups (≤5 kg, 5 to 10 kg, 10 to 25 kg, 25 to 45 kg and ≥45 kg). In addition to the ECG parameters, clinical data such as gender, age and body weight were also compiled. The determination of body surface area (BSA) was performed as follows: BSA (m²) = (10.1 x BW^0.67) x 10^-4. A significant correlation was found (p<0.0001) between HR, weight, and BSA when the groups were analyzed in a unified manner. There was an inverse correlation between HR and body weight. Weight was associated with changes in ECG variables; age and gender were associated with changes in heart rate.