Biomarker for cardiac aging;  knockout leads to enhanced cardiac protection after myocardial infarction in mice;  elevated MMP9 concentrations were measured in serum and saliva of patients with cardiovascular disease;  increased expression of MMP9 mRNA in the gingiva of old (>60 years) compared to young (17–20 years) patients. The gene discussed is MMP9; the disease is myocardial infarction.