Abstract: AIM: To explore the relationship between plasma myeloperoxidase (MPO) levels and the severity of chronic heart failure (CHF). METHODS: Plasma MPO concentrations were measured by ELISA in 74 consecutive patients with New York Heart Association Class II-IV chronic systolic heart failure (HF) and 55 controls (no history of heart failure). The relationship between the plasma MPO levels and CHF was analyzed by multiple linear regression. RESULTS: After adjusting for confounders, plasma MPO levels in patients with chronic systolic HF were significantly elevated compared with those in the control group ［(16±5) vs.(9±4) μg/L, P<0.01］. Furthermore, plasma MPO levels elevated with the increase of the New York Heart Association Class (Spearma’s r=0.34, P<0.01). CONCLUSION: Plasma MPO levels are elevated in patients with chronic systolic HF and the elevation is associated with the severity of HF.