Ambulatory patients attending heart failure clinics at Mount Sinai, University Health Network, Trillium Health Centre and St. Michael's Hospital with systolic heart failure (NYHA class II-IV, left ventricular ejection fraction <45%) will be screened for eligibility to participate in our randomized trial. We will randomize seventy eligible patients using a stratified, permuted block randomization scheme, to be given either 100mg BID of thiamin HCl or a matching placebo BID in a 1:1 ratio to be taken for six months. All study personnel will be blinded to treatment assignment.