['The use of trastuzumab, an antibody against the human epidermal growth factor receptor 2 (HER2), in patients with HER2 positive metastatic breast cancer, is related to cardiotoxicity.', 'To investigate whether serum HER2 is increased in heart failure patients and related to disease severity.', 'Serum HER2, plasma tumor necrosis factor (TNF)-alpha and its soluble (s) receptors (sTNF-R1 and 2) were determined with ELISA in chronic heart failure patients and age and gender-matched healthy controls.', 'Serum HER2 was higher (P=0.013) in 50 heart failure patients (18 female; median age 57 (range 33-77) years), mean 12.1+/-S.D. 2.3 ng/mL, than in 15 controls, 10.4+/-2.6 ng/mL. Serum HER2 levels correlated inversely with left ventricular ejection fraction (P=0.037) and were highest among NYHA class III patients, followed by NYHA class II patients and controls (P=0.029, Kruskal-Wallis test). STNF-R1 (P<.001) and sTNF-R2 (P=0.015) were higher in patients than controls, and correlated positively with HER2 (P=0.027 and P=0.036, respectively).'] Are serum HER2 levels increased in patients with chronic heart failure?