This clinical study was performed to evaluate the effects of Duraflo II heparin coated cardiopulmonary bypass equipment on platelet and coagulation/fibrinolysis activation. Twenty-four patients undergoing coronary artery bypass grafting were assigned to two groups using either heparin coated (Duraflo group, n = 13) or uncoated equipment (control group, n = 11). In the Duraflo group, the cardiotomy reservoir was also coated with heparin. Standard systemic heparinization was performed in both groups. There were no significant differences in activated clotting times or plasma free hemoglobin concentrations between the two groups. Platelet loss and platelet activation, as measured by increases in plasma beta-thromboglobulin (beta-TG) and platelet factor 4 (PF4), in the Duraflo group (beta-TG:237 +/- 143 ng/ml, PF4:167 +/- 104 ng/ml at the end of cardiopulmonary bypass) were less than those in the control group (beta-TG:373 +/- 131 ng/ml, PF4:295 +/- 131 ng/ml at the end of cardiopulmonary bypass). No significant differences were found in thrombin-antithrombin III complex levels or alpha 2 plasmin inhibitor-plasmin complex levels between the groups. Therefore, the use of Duraflo II heparin coated equipment with a heparin coated cardiotomy reservoir suppressed platelet activation.