Abstract: OBJECTIVE To explore the correlation between the changes of matrix metalloproteinases (MMPs), neutrophil CD₆₄, interleukin-17 (IL-17) and interleukin-21 (IL-21) and the myocardial function of the heart failure children with pulmonary infection. METHODS Totally 148 heart failure children who were complicated with pulmonary infection and treated in Tianjin Children's Hospital from Jan 2016 to Aug 2018 were chosen as the infection group, meanwhile, 150 heart failure children who were not complicated with pulmonary infection were assigned as the non-infection group. The levels of MMPs, myocardial enzymes and other serological factors were compared between the two groups, and the correlation between the MMPs, CD₆₄, IL-17, IL-21 of the patients in the infection group and the myocardial function was observed. RESULTS The levels of MMP-2, MMP-9, MMP-10, IL-7 and TNF-α of the infection group were significantly higher than those of the non-infection group (P<0.001). The levels of CK, AST, CKMB,LDH, CD₆₄ and PCT of the infection group were significantly higher than those of the non-infection group (P<0.001). In the infection group, the levels of MMP-2, MMP-9, MMP-10, CD₆₄ and IL-17 of the patients with grade NYHA-Ⅰ and Ⅱ were significantly lower than those of the patients with grade NYHA-Ⅲ and Ⅳ (P<0.05 or P<0.001). There was no significant difference in the IL-21 level between the two groups. CONCLUSION The sensitive changes of MMPs, CD₆₄, IL-17 and IL-21 may reflect the myocardial function and severity of pulmonary infection in the heart failure children complicated with pulmonary infection, which have certain clinical value in prediction of illness condition.