Currently, there is no doubt that the problem of electrical instability of the myocardium in pediatric cardiology is relevant. The determination of various indicators of electrical instability of the myocardium, which are predictors of life-threatening rhythm disorders and sudden cardiac death, presents an underdeveloped task not only for functional diagnostics specialists, but also for pediatricians, neonatologists, pediatric cardiologists and doctors of other specialties. Non-invasive research methods such as electrocardiography (ECG), Holter ECG monitoring (HM ECG), available in almost all pediatric treatment and prevention institutions, are quite informative in terms of detecting electrophysiological heterogeneity of the myocardium as a predictor of sudden cardiac death, which is especially important in children at risk, as well as young athletes. Thus, the determination of indicators of electrical instability of the myocardium is of great interest, it is a promising direction in modern clinical practice, allowing to predict the risk of developing fatal arrhythmias in children and adolescents.