Conclusions: Multivariable analysis showed that an age ≥ 64 years; the presence of atrial fibrillation, diabetes mellitus, CKD stages 1–3 and dilated cardiomyopathy; an LAVI ≥ 39 mL/m2; and serum levels of hs-CRP ≥ 6.10 mg/L, irisin ≤ 7.2 ng/mL, and visfatin ≤ 1.1 ng/mL were predictors of poor clinical outcomes in HFpEF with low levels of NT-proBNP. This evidence concerns the gene FNDC5 and atrial fibrillation.