433 patients aged 29-80 with mild to moderate heart failure entered a multicentre double-blind randomised between-patient comparison of xamoterol 200 mg twice daily, digoxin 0.125 mg twice daily, and placebo. Patients were assessed at baseline and after three months. Of 349 who completed the double-blind phase, 300 had valid exercise tests. Compared with placebo, xamoterol significantly increased exercise duration and work done on a bicycle ergometer and improved breathlessness and tiredness during daily life as assessed by visual analogue scale and by Likert scale. Digoxin showed no statistically significant advantage over placebo on any of the measures except the Likert scale. Exercise performance and work done were significantly higher with xamoterol than with digoxin.