We investigated the effects of a new selective beta 1-adrenoceptor partial agonist, ICI 118.587, on left ventricular function in 14 patients with coronary heart disease and a history of stable angina pectoris. The drug (0.2 mg/kg) increased peak left ventricular dp/dt from 1518 to 1993 mm Hg/sec (P less than 0.001) and left ventricular Vmax from 1.63 to 2.08 circ/sec (P less than 0.001), while left ventricular end-diastolic pressure decreased (P less than 0.05). Measured by echocardiography, the fractional shortening of the left ventricular minor axis diameter and the mean velocity of the left ventricular circumferential fiber shortening increased (P less than 0.001) and the cardiac index increased by 36%, reflecting increased contractility mainly in the normal left ventricular wall areas. In coronary heart disease, ICI 118.587 increased left ventricular muscle contractility and output without untoward side effects in the majority of the patients.