Inclusion Criteria:

• * Body Mass Index (BMI) \>25 kilograms / square meter (kg/m2) with plan for rhythm control of atrial fibrillation by catheter ablation
• * All subjects must be able to understand and willing to sign a written informed consent document.

Exclusion Criteria:

• * Individuals who are already taking metformin or other antidiabetic medications, including insulin
• * Known diabetes
• * Known allergy or Food and Drug Administration (FDA)-labeled contraindication to taking metformin (estimated glomerular filtration rate (eGFR)\<30 millilitres per minute (mL/min)/1.73 square meters (m2), hypersensitivity to metformin, acute or chronic metabolic acidosis)
• * Patients taking carbonic anhydrase inhibitors
• * eGFR below 30 mL/min per 1.73 m2 or other clinical diagnosis of advanced renal disease
• * Acute or chronic metabolic acidosis (serum bicarbonate \<22 milliequivalents per liter (mEq/L))
• * History of significant alcohol use (\>2 drinks/day on average)
• * History of hepatic dysfunction (serum bilirubin 1.5 times greater than ULN)
• * History of New York Heart Association (NYHA) Class III or IV heart failure
• * Pregnancy or nursing