Purpose: To detect the relationship of N-terminal pro-brain natriuretic peptide levels with clinical and laboratory findings by measuring them at diagnosis, during, and after treatment in children with acute rheumatic carditis. Method: A total of 40 children including 20 acute rheumatic carditis patients aged between 5 and 16 years 20 healthy children as controls were included in the study. Blood was drawn from patients at diagnosis and in the first week, first month and third month after treatment in order to detect pro-brain natriuretic peptide, C-reactive protein levels and erythrocyte sedimentation rates. All patients underwent echocardiography. Results: The N-terminal pro-brain natriuretic peptide levels of children with acute rheumatic carditis were significantly higher than those of the control group at diagnosis and during treatment (p < 0.05). Echocardiographic evaluation of acute rheumatic carditis patients revealed that the left atrium diameter continued to decrease during the study and that the mean left atrium diameters measured at diagnosis and in the first week were statistically higher than the mean left atrium diameters measured in the third month. There was significant correlation between left atrium diameters at diagnosis and in the first month and N-terminal pro-brain natriuretic peptide levels during the same periods in the patient group. Conclusion: Previous studies have used N-terminal pro-brain natriuretic peptide levels as a marker of enlargement of the left atrium, whereas in this study we want to emphasise its role as a marker of inflammation. This increase was significantly correlated with enlargement in the left atrium. N-terminal pro-brain natriuretic peptide levels were found to be a valuable determinant in indicating cardiac inflammation and haemodynamics.