In this prospective double blind randomised controlled trial of the effect of a parenteral infusion of thiamin before induction of anaesthesia we will investigate the effect on perioperative lactate increase as primary outcome and extent and duration of inotropic support after cardiac surgery. In addition the pharmacokinetics of a intravenous infusion of 300 mg of thiamin on erythrocyte thiamin content and the amount of thiamine excreted in the 24 hours via the urine will be determined.