Effects of xamoterol on resting and exercise haemodynamics in patients with chronic heart failure.

1. A bicycle exercise test was used to investigate functional capability and haemodynamics in 30 patients with heart failure (13 NYHA Class II, 17 Class III), before and after i.v. xamoterol (Corwin, Carwin, Corwil, Xamtol, ICI 118,587) 0.2 mg kg-1. 2. Resting heart rate fell from 78 to 74 beats min-1 (P less than 0.05) and cardiac index rose from 2.5 to 2.8 l min-1 m-2 (P less than 0.001) after xamoterol. Blood pressure fell slightly, and systemic vascular resistance was reduced. Stroke work index improved and double product decreased. There were no changes in pulmonary artery wedge pressure ejection fraction or plasma noradrenaline concentrations. 3. On exercise, xamoterol produced a considerable reduction in heart rate increase, improved stroke volume and left ventricular stroke index and lowered double product. Exercise duration increased by 10%, but this did not quite achieve statistical significance. 4. These results are consistent with the concept that a beta 1-partial adrenoceptor agonist with the level of intrinsic sympathomimetic activity (43%) of xamoterol provides moderate inotropic support at rest, and protects the heart against overstimulation on exercise, when sympathetic drive is high. 5. Reduction of double product on exercise implies a lowered oxygen demand, which could be of considerable importance in patients with ischaemic heart disease.