The FGF23 increment was higher in patients with end-stage kidney/heart failure than in other subjects (+300 pg/ml [95% CI: 41–558 pg/ml] vs. +20 pg/ml [95% CI: 12–27 pg/ml]), and was higher if baseline 25(OH)D concentrations were <50 nmol/l instead of ≥50 nmol/l (+34 pg/ml [95% CI: 18–51 pg/ml] vs. +9 pg/ml [95% CI: 3–14 pg/ml]). This evidence concerns the gene FGF23 and heart failure.