The haemodynamic effects of cicloprolol, a new partial beta 1-adrenoceptor agonist, were investigated at rest and during exercise in 10 patients with moderate heart failure. At rest, cicloprolol (0.10 mg/kg i.v.) increased heart rate by 8 p. 100 (80.6 +/- 5.7 vs 74.7 +/- 11.9 beats/min; p less than 0.05), cardiac index by 17 p. 100 (3.74 +/- 0.57 vs 3.20 +/- 0.41 l/min/m2; p less than 0.001) and stroke index by 6 p. 100 (46.3 +/- 8.3 vs 43.7 +/- 8.8 ml/beat/m2; p less than 0.05). Left ventricular end-diastolic pressure was reduced by 35 p. 100 (9.9 +/- 5.0 vs 15.2 +/- 7.4 mmHg; p less than 0.01). There were no significant changes in aortic pressure. Systemic vascular resistance decreased by 15 p. 100 (1,030.8 +/- 234.6 vs 1,209.6 +/- 319.7 dynes.s.cm-5; p less than 0.01). During moderate exercise (114 +/- 13 watts) in supine position, cicloprolol induced a 10 p. 100 reduction of tachycardia (99.7 +/- 10.2 vs 112.2 +/- 16.5 beats/min; p less than 0.01), a 6 p. 100 decrease of mean aortic pressure (112.4 +/- 19.7 vs 119.5 +/- 19.2 mmHg; p less than 0.01) and an 8 p. 100 decrease of cardiac index (5.42 +/- 0.63 vs 5.88 +/- 0.75 l/min/m2; p less than 0.001). There were no significant changes in left ventricular filling pressure and stroke index. When data obtained at rest and during exercise were pooled, an inverse linear relationship (p less than 0.01) was found between heart rate before treatment with cicloprolol and cicloprolol-induced variations in heart rate and cardiac index.(ABSTRACT TRUNCATED AT 250 WORDS)