Heart tissues of SHRs exhibited increased mRNA expression of ANP, BNP and β-MHC and protein expression of myocardial hypertrophy markers, including Collagen I, Collagen III, matrix metalloproteinase 2 (MMP 2) and matrix metalloproteinase 9 (MMP 9), compared with the age-matched WKY rats (p < 0.05). The gene discussed is MMP9; the disease is hypertrophy.