Xamoterol 200 mg twice daily was given for 2 months to nine patients with severe heart failure already being treated with angiotensin converting enzyme (ACE) inhibitors. Left ventricular end-diastolic pressure fell from 28 to 13 mmHg and end-systolic volume fell from 115 to 106 ml m-2; indices of contractility improved and ejection fraction rose from 33 to 38%. The time constant of ventricular relaxation, T1, improved from 62 to 44 ms. Exercise tolerance improved. Thus, in this group of patients with severe heart failure, xamoterol produced benefits in systolic and diastolic function. There were no adverse effects.