Thiamine Supplementation in Heart Failure: a Pilot Randomized Controlled Crossover Trial

Inclusion Criteria: * Age ≥60 * NYHA class II-IV symptoms * Recent HF-related admission in past 12 months OR NT-proBNP \>600ng/L within 60 days of screening * LVEF ≤45% on 2D/3D echocardiography or radionuclide angiography (RNA) in the past 12 months (on optimal therapy) * Medically optimized prior to enrolment with angiotensin converting enzyme inhibitor or angiotensin receptor blocker (± neprilysin inhibitor), β-blocker, and/or aldosterone antagonist at target or maximally tolerated doses. * Patients must be stable on medications without hospitalization in the past month. Exclusion Criteria: * Taking \>2.5mg/d of thiamine supplement. Allows standard multivitamin. B complex vitamin not allowed due to high thiamine content. * Unable to swallow study medication. A placebo swallowing test will take place at screening. * Clinical indication for thiamine supplementation including symptomatic thiamine deficiency (Wernicke's encephalopathy, severe malnutrition, refeeding syndrome) and heavy alcohol use, \>15 standard drinks per week in men and \>10 standard drinks per week in women. * End-stage renal disease on dialysis * Severe mitral valve disease because this impacts the accuracy of speckle tracking analysis on echocardiography. * Non-English speaking (unable to complete questionnaires). * Unable to provide written consent. * Cognitive impairment without a caregiver administering medications. * Expected survival \<1 year due to non-cardiac disease. * Expected heart transplantation in \<6 months (± left ventricular assistive device). * Allergies to the ingredients of the study medication or placebo