Cardiopulmonary bypass (n = 8 calves) with heparin-coated perfusion equipment, low-dose systemic heparinization (activated clotting time: ACT greater than 180 s) and high-dose aprotinin administration was evaluated in comparison to standard perfusion equipment with full-dose systemic heparinization (ACT greater than 480). All animals were perfused for 6 hours and similar values were observed for blood gases and mixed venous oxygen saturation in both groups. The heparin doses given in the study group before and during the 6 hours of perfusion totalized 14660 +/- 2553 IU as compared to 60833 +/- 5137 IU for the control group. No protamin was given in the study group whereas an equivalent of 27000 +/- 5805 IU was necessary to reverse heparin in the control group. There was no difference for prebypass hematocrit versus postbypass hematocrit in the two groups. Prebypass plasma hemoglobine was 8.4 +/- 2.1 mumol/L in the study group versus 10.0 +/- 3.8 mumol/L in the control group. After mixing with the priming volume, plasma hemoglobine was 8.6 +/- 2.5 mumol/L in the study group versus 6.7 +/- 1.6 mumol/L in the control group. The highest value was observed in the study group after 2 hours of perfusion (8.2 +/- 2.1 mumol/L) versus 5 hours of perfusion in the control group (7.4 +/- 3.6 mumol/L). Prebypass LDH levels of 1610 +/- 150 IU in the study group versus 1740 +/- 210 IU in the control group moved to 1870 +/- 200 IU in the study group at 24 hours after perfusion versus 2650 +/- 400 IU in the control group at 24 hours and decreased thereafter.(ABSTRACT TRUNCATED AT 250 WORDS)