Diabetes mellitus (DM) is a major risk factor for heart failure (HF), specifically for heart failure with preserved ejection fraction (HFpEF). The diagnosis of HFpEF is a complex matter, due to presence of many confounders that limit the diagnosis. Glucagon is a key player in DM pathogenesis, also, it has a positive inotropic and chronotropic effects on the failing hearts. Objective: It is of interest to investigate the role of fasting glucagon as marker for HFpEF evolution among patients with type 2 DM. Methods: This case-control study was conducted in Internal Medicine Department in collaboration with Cardiology Department and Clinical pathology Department, Faculty of Medicine, Zagazig University Hospitals. This study was conducted on 32 subject with type 2 DM and were allocated into two equal groups: Type 2 DM without HF group (control group), and Type 2 DM with HFpEF group (case group). All patients underwent trans-thoracic echocardiography, routine laboratory tests and measurement of fasting levels of serum glucagon by (ELISA) kits. Results: Diabetic patients without HF (group I) and those with HFpEF (group II) weren’t statically different as regard the basic study parameters with exception of hypertension which was significantly higher in group II. Fasting glucagon level was significantly higher in group II when compared with group I. HFpEF correlated with fasting serum glucagon in a positive manner. Also, serum glucagon showed a positive correlation with AF. Fasting glucagon (pg/ml) at cut off value of ˃ 63.56 pg/ml had a sensitivity of 93.7%, and specificity of 56.2% in predicting the presence HFpEF. Conclusion: Serum glucagon represents a clue for early detection of HFpEF among type 2 DM patients especially if measured in a serial manner.