ABSTRACT The cardiac electrical activity can be recorded through the electrocardiogram (ECG), this recording is able to capture the changes in the electric route. In the scientific literature, there is no description of electrocardiographic patterns of Wistar rats at the stage of newborn to be considered aged. The aim of this study was to evaluate the electrocardiographic pattern of Wistar rats at various stages of growth, in order for the results to contribute as a standard reference. Rattus norvegicus albinus rats of the Wistar lineage were used. The rats were divided into 5 experimental groups being defined according to age and named as follows: group 21 days (21D), 2 months (2M), 3 months (3M), 7 months (7M) and 18 months (18M), where n = 20 per group. For the realization of ECG, electrodes connected to the electrocardiograph channels were positioned in animals to capture the electrical signal of the heart in 6-lead. The data were grouped and subjected to comparison by ANOVA and Tukey-Kramer test, P=0.05. The results showed that, overall, the modulations along the front aging process, related to the ECG, are initiated from 2M period, apparent stability by 3M and/or 7M, followed by exacerbation of modulations in 7M and/or 18M, depending on the electrocardiographic variable in question. Front of heart rate (HR), concomitantly, there is a similar pattern, that is, decreasing from 2M period with stability until 7M, followed by more pronounced decrease in 18M. The results suggest that due to the aging process, the heart of Wistar rats shows changes in the conduction of electrical stimulation and reduction in heart rate, factors that deserve attention as indicators of inclusion / exclusion of animals in experimental groups by researchers using that species as a model.