Heart failure (HF) is a major cardiovascular complication of diabetes mellitus (DM). The greatest risk factor for HF is age, and data indicate that 6 to 10 % of individuals over the age of 65 years suffer from HF. Patients with DM have a 2.5-fold increased risk for developing HF than individuals without DM. The 25 to 40 % of patients with HF who have DM have worse outcome (death from cardiovascular disease or hospitalization for worsening HF) than patients without DM. Hyperglycemia is a risk factor for the development of HF with an increase in incidence of HF rising from 10 % at hemoglobin A1c (HbA1c) 8.0 to 9.0 % to 71 % at a HbA1c > 10 %. Patients with DM and HF are equally distributed between those with low ejection fractions and those with normal ejection fractions. The HF treatment regimens for patients with HF and DM (blockade of angiotensin II synthesis or action, cardioselective β-adrenergic blockade, mineralocorticoid receptor blockade, and diuretics) are the same as for HF patients without DM, though the benefit on clinical outcomes is not as great. The new angiotensin-neprilysin inhibitors appear to provide increase outcome benefits in both HF patients with or without DM. Glycemic control impacts the clinical outcomes in patients with HF and DM in a U-shaped relationship with poorer survival at low and high mean HbA1c levels. The optimal chronic glycemic control occurs at an HbA1c of 7.5 to 8.0 % for patients with DM who have symptoms of HF.