Background: Plasma levels of proinflammatory cytokines, including tumor necrosis factor (TNF)-α and interleukin (IL)-6, are elevated in patients with congestive heart failure (CHF). Recent studies suggest that the failing human heart is a source of proinflammatory cytokines in the end-stage failing heart. However, the relevance of plasma levels to those of the myocardium remains undefined. We sought to compare cytokine expression in early and end- stage CHF, and to evaluate the correlation of tissue expression to plasma levels. Methods: Two patient populations were studied: patients with recent- onset CHF, all with symptoms less than 6 months (n = 17, duration of symptoms 2.1 ± 1.6 months, range of New York Heart Association (NYHA) 1 to 3), and end-stage heart-failure patients (n = 7) who underwent left-ventricular assist-device (LVAD) implantation (Duration of symptoms 47.1 ± 28.0 months, all NYHA class 4). Plasma levels of TNF-α and IL-6 proteins were evaluated by an Enzyme-Linked Immuno-Sorbent Assay (ELISA), while myocardial levels of cytokine transcripts were assessed by ribonuclease (Rnase) protection assay. Results: In patients with end-stage heart failure, TNF-α and IL-6 were increased in the plasma as well as in the myocardium (plasma: TNF- α = 7.7 ± 2.3 pg/ml, IL-6 = 45.0 ± 47.1 pg/ml; myocardium: TNF-α = 0.31 ± 0.15% of glyceraldehyde 3-phosphate dehydrogenase (GAPDH) expression, IL-6 = 1.56 ± 1.54%). In contrast, despite elevated plasma levels of TNF-α and IL-6, the myocardium of patients with the recent onset of symptoms demonstrated minimal expression of TNF-α and IL-6 messenger ribonucleic acid (mRNA) (plasma: TNF-α = 4.3 ± 1.7 pg/ml, IL-6 = 3.3 ± 1.8 pg/ml; myocardium: TNF- α = 0.13 ± 0.04%, IL-6 = 0.02 ± 0.04%). Plasma levels of TNF-α were significantly correlated with those in the myocardium when both populations were combined. (r = 0.69, p < 0.001). Conclusions: Cytokines are expressed in the myocardium in end-stage heart failure to a much greater degree than in patients with the recent-onset of symptoms. This suggests that induction of cytokines in the myocardium is a relatively late event in the pathogenesis of CHF. Furthermore, plasma levels of TNF-α correlates with mRNA expression in the myocardium and thus may serve as an appropriate marker of myocardial cytokine activation. Whether the production of cytokines in the failing human heart precedes the elevation of cytokines in the plasma remains undefined. Therefore, we studied expression of TNF-α and IL-6 in the myocardium as well as in the plasma in patients with early and end-stage CHF. The results have demonstrated that cytokines are expressed in the myocardium in end-stage heart failure to a much greater degree than in patients with the recent onset of symptoms. This suggests that induction of cytokines in the myocardium is a relatively late event in the pathogenesis of CHF.