This is a double-blind, placebo-controlled, cross-over study evaluating the effects of UDCA on peripheral blood flow and immune function in patients with stable chronic heart failure (CHF). Sixteen patients with CHF will be recruited from the heart failure clinic at the Royal Brompton Hospital. Following baseline evaluation, patients will be randomised to receive either placebo or UDCA at a dose of 1000 mg/day for a period of four weeks. They will then undergo repeat evaluation (peripheral blood flow and immune function). A four week washout period will then take place before the patients cross-over to receive the respective other therapy for a further four weeks (i.e. those first receiving placebo will go onto receive UDCA and vice versa). The study will be completed after a total of twelve weeks, with a final assessment (peripheral blood flow and immune function).