Coating of cardiopulmonary bypass circuits may be a solution to prevent adverse effects induced by contact of blood elements with foreign surfaces. Using an animal model, we investigated the Trillium TM coating of cardiopulmonary bypass circuits (a new process involving polyethylene oxide, sulphonate groups and heparin) at low systemic heparinization, focusing on haemolysis and clot formation. Cardiopulmonary bypass was initiated through jugulo-carotid access with ACT maintained around 180 sec. Treated circuits (Trillium group) were evaluated in 3 calves (mean weight of 66.0+/-8.7 kg), vs. untreated circuits in 3 control calves (mean weight of 60.7+/-7.5 kg). Blood samples were drawn at regular intervals for biochemical, hematological and blood gas analyses. After 6 consecutive hours, the animals were weaned from CPB and were awakened. The circuits were analyzed for clot deposits. After 7 days the animals were sacrificed and an autopsy was carried out. Red cell and white cell counts did not change over the 6 hours. Platelet counts dropped to 75.9+/-7.3% of the baseline value in the Trillium group after 6 hours whereas counts dropped to 57.2+/-26.0 in the control group (p<0.05). Plasma free Hb remained constant in the Trillium group but increased significantly to 280+/-65% of baseline value in the control group (p<0.05). The amount of clots were significantly higher in the control group, in the connectors, the reservoir, the heat exchanger, and the oxygenator. No renal emboli were seen in the Trillium group whereas the mean number of emboli was 3.0+/-2.4 in the control group. We conclude that Trillium coating significantly improves the biocompatibility of artificial surfaces exposed to blood.