Twenty patients with severe chronic cardiac failure caused by ischaemic heart disease were treated with flosequinan 100 mg daily or placebo in addition to their existing treatment with diuretics and, in some, digoxin in a randomised double blind trial. After eight weeks of treatment, flosequinan significantly improved treadmill exercise time, increased peak achieved oxygen consumption, and improved the New York Heart Association symptom grade when compared with placebo. One patient in the placebo group died and another was withdrawn because heart failure worsened. One patient in the flosequinan group was lost to follow up but there were no other withdrawals. Flosequinan was well tolerated with few adverse effects, and it may prove to be a useful addition to diuretics and digoxin in the treatment of chronic cardiac failure.