Background : Carbohydrate Antigen 125 (CA 125), a marker for ovarian cancer, has been reported to increase in relation to the severity of heart failure. The aim of this study was to evaluate the serum levels of CA 125 in patients with idiopathic dilated cardiomyopathy (DCM). Method : Serum levels of CA125 were obtained in 68 patients (41 males and 27 females; age 52짹14 years) with DCM (left ventricular ejection fraction 22.3짹7.5%). Results : The mean value of CA 125 was 91.3짹115.4 U/ml (range 4 to 471): 101.2짹76.2 in men and 76.2짹100.3 in women (p=0.386). CA 125 above the normal value (<35 U/ml) was found in 37 (46%) of 68 patients. Patients with >35 U/ml of CA 125 were younger (49짹16 vs 57짹11 years, p=0.02), and had advanced New Yourk Heart Association functional class, higher serum levels of N-terminal pro-brain natriuretic peptide (NT-proBNP, 6274.6짹6536.0 vs 2747.5짹2666.2 pg/mL, p=0.004) and lower deceleration time of early filling mitral inflow (116.7짹28.2 vs 172.1짹73.5, p<0.001). Serum levels of CA 125 were well correlated with age, serum levels of NT-proBNP and percent of neutrophil in multivariate linear regression analysis (table). Conclusion : CA 125 was markedly elevated in patients with DCM and correlated with heart failure severity and serum NT-proBNP. Therefore, measurement of CA 125 might be an additional tool in the management of patients with heart failure.