ICI 118/587 is a partial agonist of beta 1 adrenergic receptors, a partial agonist being an agent which has both agonist and antagonist properties. The agonist properties of ICI 118/587 stabilise 43 p. 100 of the maximal activity of the beta 1 receptors whilst preventing a resulting increase in sympathetic stimulation. The aim of this study was to evaluate the effects of this new inotropic agent on left ventricular function and metabolism in patients with chronic myocardial infarction and left ventricular dysfunction. The study of LV function was performed in an initial group of 14 patients. After control left ventriculography, the injection of 0,1 mg/kg of ICI 118/587 increased the peak dP/dt by 35 p. 100 (p less than 0,005), reduced mean systolic parietal stress by 8 p. 100 (p less than 0,05) and LV end systolic volume from 58 to 53 ml/m2 (p less than 0,05). The global ejection fraction rose slightly, largely due to increases in the regional ejection fractions of abnormal segments (from 20 +/- 5 p. 100 to 26 +/- 5 p. 100, p less than 0,02). Left ventricular diastolic function also improved as shown by a 38 p. 100 fall (p less than 0,001) in mean diastolic stress and an increase in the time constant of isovolumic relaxation. The metabolic effects of ICI 118/587 were assessed in a second group of 11 patients with anterior myocardial infarction.(ABSTRACT TRUNCATED AT 250 WORDS)