['The level of copeptin, a stable fragment of pro-arginine-vasopressin (AVP), correlates with disease severity. It is an established, short-term prognostic marker for patients with heart failure with reduced ejection fraction (HFREF). We aimed to examine the association between copeptin and long-term mortality. We also studied the clinical usefulness of copeptin as a prognostic biomarker by analysing the improvement of net reclassification.', 'Copeptin concentrations were measured in a cohort of 195 consecutive patients with HFREF. Disease severity and clinical parameters were determined at baseline, and all-cause mortality was recorded after five-year follow-up.', 'One hundred and ten patients died during the five-year follow-up (five-year mortality rate: 0.56). Univariate analysis identified copeptin (HR 2.168 [95% CI 1.740-2.700]) as a predictor of mortality. The final, multivariable Cox survival model identified a number of independent predictors of death. These included higher NHYA functional class, previous MI, at least one hospitalisation for worsening HF (within the two years before inclusion into the study), elevated blood urea nitrogen, NT-proBNP-, and copeptin levels, as well as increased red blood cell distribution width, and decreased GFR. The addition of copeptin alone to the baseline predictive model (NT-proBNP only) resulted in a minor (8.21%) improvement, whereas the final, multivariable model showed a significant increase in net reclassification (10.26%, p=0.015).'] Is copeptin ( C-terminal pro arginine-vasopressin ) an independent long-term prognostic marker in heart failure with reduced ejection fraction?