Background: The impact of matrix metalloproteinase (MMP) on left ventricular (LV) remodeling and heart failure events is unresolved in patients with hypertrophic cardiomyopathy (HCM). Methods and Results: Plasma levels of MMP-2, MMP-9, tissue inhibitor of metalloproteinase (TIMP)-1 and clinical findings and heart failure events were evaluated in 41 HCM patients, including 8 with LV systolic impairment. Plasma B-type natriuretic peptide (BNP) levels were also measured. MMP-2 levels in patients with severe symptoms were higher than that in those with no or mild symptoms. The levels of MMP-2 and TIMP-1 were positively related to LV end-systolic and left atrial dimensions, and inversely related to LV ejection fraction. MMP-2 levels were positively related to BNP levels (r=0.52, P=0.0009). However, MMP-9 levels were not related to echocardiographic parameters and plasma BNP levels. Six patients had complicated heart failure events during the follow-up period of 3.2±0.7 years. Patients with high plasma MMP-2 levels (>1,170 ng/ml) revealed a poorer prognosis than those with low MMP-2 levels. Conclusions: Elevated levels of MMP-2 were related to LV remodeling and poor prognosis in patients with HCM. These results suggest that regulation of the extracellular collagen matrix might be one of the therapeutic targets in patients with HCM.  (Circ J 2010; 74: 1191 - 1196)