Levosimendan, a novel calcium sensitizer, enhances cardiac contractility by increasing myocyte sensitivity to calcium, and induces vasodilation. In this prospective observational study the haemodynamic effects of levosimendan in postoperative critically ill patients are reported. Twelve patients with the need for inotropic support were studied. One dose of levosimendan (12.5 mg) was administered at a rate of 0.1-0.2 microg kg(-1).min(-1), either alone or in addition to pre-existing inotropic therapy. Haemodynamic measurements were obtained at baseline, and at 3 h, 6 h, 12 h, and 24 h after the start of the levosimendan infusion. Levosimendan significantly increased cardiac output from (mean+/-SD) 4.3+/-0.91.min(-1) to 5.2+/-1.51 min(-1) after 24h (P=0.013), by increases in stroke volume (baseline 47+/-15 ml, after 24h 57+/-25 ml, P=0.05), as heart rate remained unchanged. Systemic vascular resistance decreased from 1239+/-430 dyn.sec.cm(-5) at baseline to 963+/-322 dyn.sec. cm(-5) at 24h (P<0.001). Pre-existing inotropic therapy present in ten patients remained unchanged or was reduced. In postoperative critically ill patients, infusion of levosimendan exerted favourable haemodynamic responses. Levosimendan increased cardiac output by increasing stroke volume, which might be attributed primarily to its inotropic properties. Due to its cyclic adenosine monophosphate independent positive inotropic effects, levosimendan may be of value as adjunctive therapy to other inotropic drugs in critically ill patients.