The main findings of this study are as follows: (1) the incidence of low NT-proBNP levels in patients hospitalized with HFpEF was 13.7%; (2) age, BMI, atrial fibrillation, NYHA functional class, and albumin were independent predictors of low NT-proBNP levels in patients with HFpEF; (3) patients with HFpEF and low NT-proBNP levels had a lower risk of all-cause death or heart transplantation compared to those with elevated NT-proBNP levels, particularly in younger, male, and non-atrial fibrillation patients. This evidence concerns the gene NPPB and atrial fibrillation.