Hydroxyethyl starch or hetastarch (HES), a synthetic colloid for intravascular volume expansion, was compared with albumin after coronary artery operations in 30 patients (15 in each study group). Cardiac index, atrial pressures, heart rate, and systolic blood pressure were similar in both groups. There were no differences in cumulative urine output at 24 hours or in weight change during the first 7 postoperative days. Values for colloid osmotic pressure, as well as for this variable minus left atrial pressure, were lowest soon after bypass but returned to baseline within 4 hours, with no difference between groups in the first 24 hours or 7 days after operation. Coagulation variables were similar, but prothrombin and partial thromboplastin times were higher 12 hours postoperatively and fibrinogen level was lower 7 days postoperatively in the patients receiving HES. There was no clinical evidence of excessive bleeding, although cumulative chest drainage at 12 and 24 hours was slightly higher in the HES group (p = 0.09 and 0.08, respectively). We conclude that hetastarch is a safe and effective colloid to use following coronary operations. © 1984, The Society of Thoracic Surgeons. All rights reserved.