Abstract
The clinical picture at the initial stage of pulmonary arterial hypertension is scanty and nonspecific, especially in young children, which makes it difficult to diagnose PAH and control the course of the disease. On average 2.5 years pass before the appearance of pronounced clinical symptoms and diagnosis, when there are already irreversible changes in the pulmonary artery vascular wall. We present the results of studying the concentration of 5-hydroxyindoleacetic acid (5-HIAA) in blood plasma in young children with PAH before and after surgical correction of congenital heart defects. The revealed increase of 5-HIAA in plasma in children in the early postoperative period can be used in the diagnosis of PAH and serve as a criterion for assessing the regression of pulmonary hypertension.