Aim: evaluation of the intracardiac hemodynamics and determination indications for early correction of the atrial septal defect in children before 1 year age.Methods. The study included patients observed from 2010 to 2021. The first group was formed from children under the age of 12 months with ASD and were observed for the next 4 years until its interventional or surgical elimination. The second group included healthy children of the appropriate age. All patients underwent an echocardiographic (ECHO) study with assessment of the main parameters of hemodynamics and intracardial structures.Results. The first group included 887 children with ASD, the control group included 887 healthy children. The age of the patients included in the study was 6 ± 2.6 months. for group I and 6 ± 2.5 months. for the second one. It was found that in young children with ASD, the first manifestation of hemodynamic changes was dilatation of the right ventricle, then the right atrium and finally dilatation of the pulmonary trunk, which was accompanied by an increase in pressure in the pulmonary circulation and weight loss. In 11% of patients, spontaneous closure of the ASD occurs within the first year of life. Almost 20% of patients are younger than 6 months. have clinical and hemodynamic indications for surgical treatment of ASD.Conclusions. Indications for the atrial septal defect closure should be determined taking into account clinical, anatomical and hemodynamic parameters.