Differences in hemodynamic stability and fluid requirements were examined in patients randomly assigned to receive either normal saline crystalloid solution (N = 10) or hetastarch colloid solution (N = 11) after coronary artery bypass or valve operation. Both solutions were administered in the same manner for 8 hours after surgery, with hourly assessment of hemodynamic parameters and intake/output data. Infusion rates and 8-hour intake were higher for the group receiving normal saline solution (p less than 0.001), as was postoperative weight gain (p less than 0.01), although urine and chest tube outputs did not differ. Despite lower filling pressures, subjects receiving hetastarch exhibited higher systolic blood pressures and cardiac outputs (p less than 0.05). Hematocrits on postoperative day 1 were lower in the group given hetastarch (p less than 0.001), suggesting prolonged intravascular expansion. The subjects given hetastarch also required significantly less time in the intensive care unit (p less than 0.001). Thus, cardiac surgical patients receiving colloids exhibited reduced fluid requirements, superior hemodynamic performance, and shortened intensive care stay when compared with those given crystalloid resuscitation.