In 46 children with heart defects of the Fallot group upon admission to the hospital and on the operating table, the concentration of the main classes of immunoglobulins M, G, A was studied in the blood serum by the method of radial immunodiffusion. It was found that according to the content of immunoglobulins, patients can be divided into 3 groups: with normal, decreased and high immunological indicators. During their stay in the hospital prior to the surgical correction of the heart defect, no improvement in the content of immunoglobulins was observed. On the contrary, in patients with reduced immunological parameters, there was a further decrease in the amount of IgG.