Background:The defeat of the cardiovascular system is considered a proven comorbid state in rheumatic diseases, including rheumatoid arthritis in adults. One of the markers of the cardiovascular failure formation is BNP, namely, its N-terminal inactive fragment (NT-proBNP76), which accumulates in specific granules of cardiomyocytes. Its diagnostic value increases with the appearance of minimally expressed symptoms. The long-term course of JIA is also characterized by changes in the state of the cardiovascular system, and there may be no visible clinical manifestations. For their diagnosis a 6-minute walk test is widely used, including in children.Objectives:To study the content of NT-proBNP in patients with juvenile idiopathic arthritis and compare with the level of exercise tolerance.Methods:10 patients with JIA (9 girls, 1 boy), average age 12.78 ± 0.95 years, were examined. All children had a polyarticular RF negative subtype of JIA with a disease duration of more than three years (average disease duration 69.56 ± 17.07 months), received basic methotrexate therapy and did not have dysfunction of the lower extremities joints. The control group included 7 healthy children, comparable by sex, average age 14.25±0.73 years. An ECG, an ultrasound scan of the heart, and a 6-minute walk test (6MTX) were carried out with determining the distance traveled (6MWD) and the increase in heart rate. The level of the N-terminal polypeptide of cerebral natriuretic hormone (B-type) (NT-proBNP) was determined in the morning, after waking up, and studied by competitive immunoassay on an IMMULITE 2000 analyzer (“Siemens”).Results:In children with JIA a decrease in myocardial contractility was not detected. Left ventricular ejection fraction (62.17±0.83% (60.02 – 64.02) versus 69.84 ± 0.85% (62.3 – 80.3), p <0.05) in children with JIA were within normal limits, but significantly lower than in the control group. According to the results 6MTX indicator 6MWD in JIA-patients was 490.51 ± 11.40 m and in the control group 516.85 ± 8.84 m (p <0.05) and heart rate growth was 27.75 ± 2.30% versus in the control group (37.38 ± 3.86%), p <0.05. A negative correlation between the increase in heart rate and the duration of the disease was found (r = -0.7, p = 0.05). The level of NT-proBNP in patients with JIA was within physiological values and amounted to 47.5 ± 14.09 pg / ml (20 – 128 pg/ml), but this was higher than in children of the control group (20.29 ± 0.29 pg / ml (20-22 pg/ml), p <0.05). A high correlation was found between 6 MWD and NT-proBNP level (r = 0.8, p <0.03).Conclusion:In children with JIA there is a decrease of the exercise tolerance that increases with the duration of JIA on the background of preserved myocardial contractility. This is accompanied by a higher basal NT-proBNP level than in healthy children.Disclosure of Interests:None declared