Abstract: AIM:To investigate the effect of blocking peroxisome proliferator activated receptor β/δ (PPARβ/δ) signal channel on the action of atorvastatin in inhibiting matrix metalloproteinase9 (MMP-9) expression in cardiomyocytes of aging rats. METHODS: Primary cardiomyocytes were cultured in aging rats. Cardiomyocytes were divided into control group, dimethyl sulfoxide (DMSO) group, atorvastatin group and atorvastatin plus GSK0660 group, which were treated by cell culture medium, DMSO, atorvastatin, and atorvastin plus GSK0660, respectively. Expression of MMP-9 mRNA was evaluated by RTPCR and the content of MMP-9 protein was detected by Western blot. RESULTS: No difference was observed in the expression level of MMP-9 mRNA and protein between control group and DMSO group. Expression level of MMP-9 mRNA and MMP-9 protein in atorvastatin group was significantly lower than in control group (P<0.01). Both mRNA and protein expression levels of MMP-9 in atorvastatin plus GSK0660 group were higher than in atorvastatin group (P<0.05 or P<0.01) but still lower than those in control group (P<0.05). CONCLUSIONS: Atorvastatin downregulates the expression of MMP-9 in aging cardiomyocytes by activating PPARβ/δ signal channel.