Sequential hemodynamic effects of intravenous pimobendan (UD-CG 115 BS), a novel compound with positive inotropic and vasodilating properties, were investigated during left heart catheterization in nine patients with left ventricular dysfunction (ejection fraction less than or equal to 40%) and moderate congestive heart failure (NYHA classes II and III). Studies were carried out before (C) and for 60 min after intravenous administration of 5 mg of pimobendan over 1 min. Pimobendan immediately and progressively reduced systemic resistance [16 and 28% at 10 and 60 min postdrug, respectively (p less than 0.05 vs. C)] and left ventricular end diastolic pressure [from 24 +/- 3 (C) to 12 +/- 3 mm Hg at 60 min, p less than 0.001)]. Cardiac output gradually increased by 24%, but stroke volume did not, due to an equally progressive 14% rise in heart rate, whereas stroke work increased by 21% (all p less than 0.05 vs. C). Both contractility and relaxation, measured at fixed heart rates, significantly improved by 30 and 20%, respectively, at 50 min postdrug. Thus, pimobendan has immediate and prolonged arterial vasodilating effects, together with positive inotropic and lusitropic properties, resulting in an early but sustained improvement of left ventricular pump function and filling pressures.