NPPB and aortic stenosis: Fig. 1D show DPP4 levels according to categorized cardiac indexes. Thus, patients with low-flow low-gradient AS and NYHA ≥ 3 had lower DPP4 levels. Nine patients used DPP4 inhibitors, but no difference in DPP4 levels was observed when comparing user and non-users. Although there was no significant correlation between DPP4 and NT-proBNP in the patient group as a whole (Fig. 1E), there was a trend towards a negative correlation between DPP4 and NT-proBNP in patients with AS and ATTR-CM (r = -0.63, p = 0.07).