Trillium coating (Medtronic Inc., Minneapolis, MN) offers, in addition to the presence of heparin, endothelium-like properties of its negatively charged surface. Its thromboresistant properties on coated connectors are tested here and compared with uncoated standard connectors, as well as with the Carmeda BioActive surface (CBAS) heparin surface coating. A partial cardiopulmonary bypass bovine model (body weight 68 +/- 5 kg) was selected, and the surfaces were exposed to the blood stream (pump flow 3.5 L/min) for up to 350 minutes without systemic heparinization. Thereafter, another set of samples was exposed to stagnant blood for 20 minutes. Besides hemodynamic, hematologic, and biochemical analyses, the macroscopic appearance of 45 blood exposed surface samples were graded semiquantitatively on a scale of 0 to 10: no macroscopic deposits = grade 0, one spot (1 mm diameter) = grade 1, two spots = grade 2, five or more spots = grade 5, 10% of the surface covered with clots = grade 6, 100% covered = grade 10. When exposed to blood flow, Trillium and CBAS coatings showed a statistically significant (p = 0.03) better thromboresistance (score: 0 +/- 0 for both) than uncoated connectors (score: 0.8 +/- 1.5) in this nonheparinized model. The same holds true when the connectors were exposed to stagnant blood (score: 0 +/- 0 for both coatings vs 4.3 +/- 2.8 for controls; p = 0.03). Therefore, Trillium coating exhibits significant antithrombotic properties that outperform standards for connectors used in clinical perfusion.