(8-OHdG), a marker of oxidative stress, was related to LV remodeling in dilated cardiomyopathy (DCM). Methods: We performed full study of cardiac catheterization including endomyocardial biopsy from LV in 35 patients with DCM (left ventricular ejection fraction (LVEF)52865%). Biopsy samples were stained with sirius red to evaluate myocardial fibrosis, and also stained with immunohistochemical method using anti-8-OHdG antibody to evaluate myocardial oxidative stress. In 150 DCM patients, moreover, we examined whether urinary 8-OHdG levels correlated with LVEF, LV end-diastolic volume index (LVEDVI) and LV mass index (LVMI), peak early diastolic mitral annulus velocity (e’)by echocardiography. Results: Biopsy samples data showed that the ratio of oxidized nuclei in cardiomyocytes and CVF were significantly increased in patients with DCM as compared with normal subjects. A direct correlation was found between the positive staining ratio of nuclei and CVF (n535, r50.64, P!0.001). Urinary 8-OHdG was also significantly higher in DCM patients than in control subjects (DCM; n5150: 13.5 63.1 ng/ml vs control; n530: 8.061.9 ng/ml, P!0.001). There was a significant correlation between urinary 8-OHdG and LVEF, or LVEDVI, e’. Conclusions: These findings suggest that urinary 8-OHdG may be a clinically-useful marker for LV remodeling associated with DCM.