Objectives: Endothelin-1 (ET-1), plays an important role in the pathophysiology of CHF and the pulmonary endothelium is an early hemodynamic target in diastolic left ventricular dysfunction. Therefore we hypothesized that the lung is a main source of humoral endothelin in CHF and that its secretion is proportional to the degree of heart failure. Methods and results: We used rats with coronary artery ligation as an experimental model of either compensated or decompensated heart failure, depending on infarct size. Reverse transcriptase polymerase chain reaction (RT-PCR) revealed that in the lung, the expression of preproET-1 mRNA was higher in decompensated HF than in control and compensated HF rats (P<0.001). Run-on assay demonstrated that ET-1 overexpression is regulated at a transcriptional level (P<0.01). In contrast, there was no change in ET-1 mRNA expression in aortae, left ventricular myocardium and skeletal muscle. The expression of endothelin-converting enzyme (ECE)-1 mRNA was not modified and the expression of ETB receptor mRNA in the congestive lung was significantly lower than in control and compensated HF rats (P<0.0001), while the expression of ETA receptor mRNA did not differ between groups. The lung and plasma ET-1 peptide levels were respectively 4.2 and 9 fold higher in the rats with decompensated HF than in control rats (P<0.05; P<0.0001). Organoculture experiments showed that the lung ET-1 peptide secretion level in rats with decompensated HF was higher than that in control rats (P<0.01). In contrast, there was no change in ET-1 peptide secretion by the left ventricular myocardium and skeletal muscle. In plasma of rats with decompensated HF, the rate of bigET-1 conversion to ET-1 was 22%. ET-1 peptide was also present in the pleural effusion of decompensated heart failure. Plasma ET-1 concentration was significantly correlated with upstream markers of left ventricular diastolic dysfunction, with the expression of preproET-1 mRNA in the lung, with lung and pleural ET-1 concentration and with the expression ratio of ET-1/ETB receptor mRNA. Conclusion: Taken together, these data suggest that overexpression of ET-1 and down-regulation of ETB receptors in the lung are determinants of circulating endothelin in CHF. As a corollary, increased plasma endothelin may provide evidence of pulmonary endothelial dysfunction in CHF.