Sulmazol (AR-L 115 BS) is a new positive inotropic agent with arterial and venous vasodilator properties. The authors studied the effects of a 24 hours intravenous infusion (an injection of 0.5 mg/kg over 1 minute, followed by an infusion of 1.4 mg/min) on the major haemodynamic parameters of 17 patients with heart failure: 10 patients with chronic decompensation (group I) and 7 patients with heart failure as a result of acute myocardial infraction (group II). The haemodynamic criteria of inclusion were a cardiac index less than or equal to 2.5 l/min/m2 and a pulmonary capillary pressure greater than or equal to 18 mm Hg. After 6 hr of the infusion, the cardiac index increased in both groups (45%, p less than 0.001 and 40%, p less than 0.001 respectively); the pulmonary capillary pressure decreased (32%, p less than 0.001 and 30%, p less than 0.001) and the right atrial pressure decreased (51%, p less than 0.005 and 31%, NS). The total systemic resistance was also decreased (32%, p less than 0.001 and 34%, p less than 0.001), but there was no significant change in the systolic blood pressure. The heart rate increased only in group II (17%, p less than 0.001). These beneficial hemodynamic effects lasted for the 24 hours of the infusion. Sulmazol was therefore found to be very effective in the treatment of acute and chronic heart failure; its long term tolerance still needs to be demonstrated.