Objective. To evaluate the features of the cardiovascular system in children after surgical correction of congenital heart defects revealed by functional diagnostic studies.Materials and methods. A functional diagnostic examination of the cardiovascular system (CVS) was performed in 43 children aged 5 to 17 years with the main clinical diagnosis: “Congenital heart disease” (CHD), of which 33 children of the main group (MG) had corrected CHD, in 10 children of the comparison group (CG) CHD correction was not performed due to the presence of certain contraindications. Patients were on a routine examination and treatment for CHD in the cardio-rheumatology department of the institution “Gomel Regional Children’s Clinical Hospital” in the period 2020-2022.Results. Based on the statistical processing of the results of the study, which included an assessment of clinical and anamnestic data and indicators of functional diagnostic methods for examining the CVS in children with CHD, the need for a comprehensive cardiological examination in children with this pathology was established, regardless of the method of performed surgical intervention. It was found that the majority of children with corrected CHD on the ECG had rhythm and conduction disturbances, as well as combined arrhythmias, and one third of the patients had cardiac complaints. According to the Holter monitoring (HM) and bicycle ergometry (BEM) tests, the children showed signs of electrical instability of the myocardium and a decrease in the adaptive reserves of the cardiovascular system.Conclusion. Children with corrected CHD require a comprehensive functional and diagnostic examination, which makes it possible to identify an “arrhythmogenic substrate” and establish signs of myocardial electrical instability, thereby optimizing the tactics of treatment and rehabilitation of this group of patients.