In cardiovascular disorders, the myocardium may be subjected to the breakdown and remodeling of collagen by metalloproteinase-9 (MMP-9). We hypothesized that the serum MMP-9 concentration may be elevated in pediatric patients with rheumatic heart disease (RHD) and heart failure (HF), and its level can be correlated with the HF severity. Thus, in the present study, we aimed to evaluate the sensitivity and accuracy of MMP-9 to predict HF in children with RHD and to determine its effectiveness as an indicator of the degree of HF. This study included 98 consecutive children admitted to the