The results of investigations of 50 patients with tetralogy of Fallot aged from 5 months to 15 years, made prior to surgery, and of 14 others, examined after palliative operations, furnished grounds for assessing hemodynamic and morphological changes in the pulmonary vessels as viewed in an age-specific aspect. The patients underwent catheterization of the heart, angiocardiography and histological investigation of the pulmonary tissue. In each age group the characteristics of the cardiac cycle in the right ventricle, minute volume and cardiac index, hemodynamic indices of the lesser circulation, pulmonary and greater circulation vessels resistance were analyzed. In the age category of up to 6 years the development of compensatory-adaptive reactions of the organism were recorded. The pressure in the pulmonary artery remained normal. Morphological alterations in the pulmonary arterial trunks were seen to occur already in the early childhood.