The electrocardiogram (ECG) is one of the most common diagnostic tools in medicine. The ECG record reflects the electrical activity of the heart and can provide information about the functional and structural characteristics of the myocardium. ECG analysis in rats is used in studies of the state of the cardiovascular system, both in physiological conditions and in scientific modeling on animals. ECG recording technique is simple, but interpretation of electrocardiographic parameters is a difficult task. This is due to a relatively small number of experimental studies, as well as a significant variation in the parameters of electrocardiography between studies. The latter is probably due to differences in the line of rats and the anesthetics used. The need for such studies is due to the ever increasing interest in ECG data in experimental physiology, pathophysiology, pre-clinical studies and the rapid development of translational research. In this article, we examined electrocardiographic parameters in rats, their normal range, and also the effect of the type of anesthesia on the change in ECG parameters. The review is limited to lines of outbred rats, Sprague Dawley and Wistar rats, since these three lines are most often used in experimental research models. The relevance of the study is due to the development of translational cardiovascular research. The study was performed on 250 outbred rats of both sexes. ECG was recorded against a background of narcotization with a mixture of tiletamine and zolepepam. The analysis and the results of our own studies demonstrate the lack of specific recommendations for the evaluation of ECG in rats. It was established that there were no sex differences in the various ECG parameters in rats. The effect of this anesthetic mixture on the variability of heart rate is determined. The duration of the PQ interval was comparable to the values obtained against the background of urethane anesthesia. At the same time, there was a significant increase in the QRS complex. The increase in the value of the QTc interval, which we showed for the first time when using this mixture of anesthetics, also attracts attention.