During end-stage heart failure, plasma levels of interleukin-6 (IL6) are elevated. This cytokine exerts a negative inotropic influence on the myocardium. The production site of IL6 is unclear. We examined the hypothesis that IL6 in end-stage heartfailure patients is produced in the myocardium itself and is differentially regulated according to etiology. Cardiac tissue was obtained from 27 patients (idiopathic dilated cardiomyopathy,(DCM) 9/6 m/f, age 46±14 y; ischemic cardiomyopathy (ICM), 11/1 m/f, age 55±8 y) at the timeof transplantation. The tissue was subjected to IL6 Northern-blot analysis. Signals were quantified by densitometric scanning after normalization to G3 PDH mRNA. Data were compared by Mann-Whitney test between DCM and ICM patients, divided by chamber origin. IL6 transcripts were found in all patients. In DCM, left-ventricular IL6 mRNA expression was higher than in ICM (p= 0.006). Median right-ventricular as well as left-and right-atrial IL6 mRNA expression was not significantly different in both groups. In summary, in endstage heart failure, IL6mRNA is consistently expressed in the myocardium. Left-ventricular expression is higher in DCM than in ICM. These data support the concept of a potentially reversible inflammatory component in the etiology of DCM which is more pronounced than in patients with ICM of comparable clinical severity.