DPP4 and diabetes mellitus: To evaluate the association between DPP-4 inhibitor use and 6-month CV mortality in patients with DM and HF, and to assess whether this association differs across HF phenotypes: HF with preserved ejection fraction (HFpEF), HF with mildly reduced ejection fraction (HFmrEF), HF with reduced ejection fraction (HFrEF).