NPPB and hydrops fetalis: The objectives of this study were to determine (1) the prognostic value of sST2 for HF and death in patients with AF; (2) the prognostic value of sST2 for HF and death in patients with AF with and without history of HF; and (3) whether the prognostic value of sST2 for HF and death in patients with AF is independent of NT‐proBNP level.