Inclusion Criteria:  Chronic heart failure (>6 months duration) Stabilized on recommended or maximally tolerated dose of ACE-I/ARB (unless contraindicated) and beta-blocker (unless contraindicated). If indicated, an aldosterone receptor antagonist should be given (unless contraindicated). Reduced ejection fraction defined as LVEF < 40% NYHA-class II or III or IV with stable symptoms for at least the past 3 months Creatinine clearance > 45 ml/min  Exclusion Criteria:  Diabetes mellitus: Diabetes will be diagnosed using the 2018 The American Diabetes Association (ADA) "Standards of Medical Care in Diabetes 15  FPG ≥126 mg/dL (7.0 mmol/L). Fasting is defined as no caloric intake for at least 8 h.* 2-h PG ≥200 mg/dL (11.1 mmol/L) during OGTT. The test should be performed as described by the WHO, using a glucose load containing the equivalent of 75-g anhydrous glucose dissolved in water. A1C ≥6.5% (48 mmol/mol). The test should be performed in a laboratory using a method that is NGSP certified and standardized to the DCCT assay.* In a patient with classic symptoms of hyperglycemia or hyperglycemic crisis, a random plasma glucose ≥200 mg/dL (11.1 mmol/L). Any oral or injectable hypoglycemic therapy (e.g. insulin, sulfonylureas) Recent Hospitalizations in the past 3 months Metformin treatment within the last 3 months Creatinine clearance below 45 in the prior 6 months as assessed by Cockcroft and Gault equation Known allergy to metformin or major side effects to metformin treatment Atrial fibrillation with poorly controlled ventricular rate at rest (> 100 beats/min) Hypertrophic cardiomyopathy