MMP9 and chronic thromboembolic pulmonary hypertension: When the rats suffered from CTEPH and right ventricular hypertrophy, the expression of MMP-2 and MMP-9 in Group C was significantly lower than that in Group A, B and D, and was accompanied by significant myocardial collagen deposition Pearson’s correlation showed that the expression of MMP-2 and MMP-9 had a negative linear correlation with the expression of collagen-I, which is consistent with previous findings [3].