The hemodynamic effect of levosimendan was compared to that of dobutamine in a trial enrolling 30 adults undergoing scheduled cardiac surgery with cardiopulmonary bypass. Fifteen patients were randomly assigned to receive levosimendan in a single dose of 18 microg x kg(-1) followed in 15 to 20 minutes by start of infusion at a rate of 0.2 microg x kg(-1) min(-1) for 24 hours (levosimendan group). Another 15 randomized patients received dobutamine infused at a rate of 7.5 microg x kg(-1) min(-1). Hemodynamic parameters were measured before starting infusion of the drug and after 24 hours of treatment. Changes in the main hemodynamic parameters were as follows. In the levosimendan group heart rate (beats/min) was 87.15 (SD 10.22) at baseline and 87.91 (6.00) at 24 hours; mean arterial pressure (mm Hg) was 83.96 (10.57) at baseline and 86.41 (13.29) after 24 hours; cardiac index (L/min/m2) was 2.21 (0.23) at baseline and 2.53 (0.35) at 24 hours; systemic vascular resistance (dyn/sec(-1)/cm(-5)) was 1436.74 (311.48) at baseline and 1378.35 (320.68) at 24 hours. In the dobutamine group heart rate (beats/min) was 84.28 (2.18) at baseline and 96.02 (9.10) after 24 hours; mean arterial pressure (mm Hg) was 83.59 (9.05) at baseline and 74.29 (6.33) at 24 hours; cardiac index (L/min/m2) was 2.16 (0.28) at baseline and) 3.02 (0.34) at 24 hours; systemic vascular resistance (dyn/sec(-1)/cm(-5)) was 1578.93 (334.88) at baseline and 1136.68 (158.60) at 24 hours. We found that mean arterial pressure and both systemic and pulmonary vascular resistance decreased significantly in the levosimendan group (P < 0.05), but not in the dobutamine group. On the other hand, both heart rate and cardiac index increased in the levosimendan group only (P < 0.05). We conclude that levosimendan improves hemodynamic stability in patients who have undergone cardiac surgery and that it is a good alternative for treating postoperative low cardiac output syndrome.