Blood tests will be taken just before the study drug is given, at 6 hours, 24 hours and 7 days post dose. These samples will be used to examine the effect of HA on HO-1 at different doses, and will verify drug safety. Any adverse effects of the drug will be evaluated, although HA has an excellent safety profile when used as it is currently licensed for acute porphyria. Urine samples will also be collected to assess inflammation and quantify urinary biomarkers of AKI. This will set the scene for a randomised clinical trial of HA in cardiac surgical patients at high risk of AKI.