Fibroblast growth factor 23 (FGF-23), a key hormone for the regulation of the phosphorus homeostasis, has also several direct effects on cardiac function. In heart failure (HF), the increase of FGF-23 participates to cardiac hypertrophy and remodeling. Measurement of the intact, biologically active hormone is now available. We determined intact FGF-23 in HF patients with reduced ejection fraction and assess its prognosis value for cardiovascular death over a long-term follow-up. We observed that intact FGF-23 is an independent predictor of cardiovascular death in HF patients and provides added value to the standard of care, natriuretic peptide, for risk estimation.