The present study was designed for ex vivo evaluation of a heparin coated hard shell venous reservoir in comparison to uncoated control reservoirs. An open chest bovine right heart bypass model (n = 9, bodyweight 72 +/- 6 kg) with passive blood drainage from the right atrium into the venous reservoir and active retransfusion into the pulmonary artery (roller pump) was selected for this purpose. Clear priming was used for the open perfusion circuit. No heparin was given before or during the evaluation period which was scheduled for 6 hours. Reservoir blood flow was at the beginning 3.5 +/- 0.6 l/min for coated versus 3.4 +/- 0.3 l/min for uncoated (NS). After 6 hours, blood flow was 3.3 +/- 0.1 l/min for coated versus 2.7 +/- 0.4 l/min for uncoated (p < 0.05). Hematocrit moved from a baseline level of 30 +/- 2% for coated versus 28 +/- 3% for uncoated (NS) to 28 +/- 3% for coated versus 27 +/- 5% for uncoated (NS) after 6 hours. Prebypass platelet levels of 100% in both groups moved to 84 +/- 3% for coated versus 78 +/- 23% for uncoated (NS) after 6 hours. Activated coagulation time (ACT) before bypass was 148 +/- 12 s for coated and 153 +/- 6 s for uncoated (NS). After 6 hours, ACT was 160 +/- 9 s for coated versus 152 +/- 5 s for uncoated (NS). Thrombin time before bypass was 15 +/- 2 s for coated versus 16 +/- 2 s for uncoated (NS).(ABSTRACT TRUNCATED AT 250 WORDS)