Colloids are useful in cardiac surgery to increase preload and improve cardiac output without the risks associated with blood transfusions. Pentastarch is a new low‐molecular weight hydroxyethyl starch compound under investigation for this purpose. The authors compared, in a randomized fashion, 12 patients who received pentastarch and 17 patients who received albumin for volume expansion after open‐heart surgery. During the 24‐hour study period there was no significant difference between the two groups with respect to systemic blood pressure, mean arterial pressure, cardiac index, right atrial pressure, and pulmonary capillary wedge pressure, with the exception of a higher mean arterial pressure and systolic blood pressure at 4 hours in the albumin group and higher heart rate at 12 hours in the pentastarch group. In addition, postoperative prothrombin time, partial thromboplastin time, fibrinogen, platelets, and factor VIII levels were not significantly different between the two groups. There were no complications attributed to colloid administration. The hemodynamic parameters were further evaluated in a subset of 6 pentastarch and 9 albumin patients who received the first 500 mL of colloid in a similar time frame and under similar clinical conditions. The patients who received pentastarch showed a significantly greater increase in cardiac index than did the patients who received albumin. No significant change in other parameters were noted between the two groups. The authors conclude that pentastarch is as safe as albumin and may be a more effective volume expander than albumin when used in open‐heart surgery p