The current study was designed to evaluate tubing sets with either polymeric phospholipids or ionically bound heparin in six bovine experiments (body weight, 70 +/- 5 kg). No heparin was given systemically. Left heart bypass was started with 300 ml of clear priming solution and maintained over 6 hours (50 ml/kg/min). Coagulation studies included platelet counts, activated coagulation time (ACT), thrombin time (TT), fibrinogen (Factor I), antithrombin III (AT III), and fibrinopeptide A (FPA). Normalized platelet levels dropped from 100 +/- 12% before to 86 +/- 13% after 6 hours of left heart bypass for heparin, compared with 100 +/- 46% to 90 +/- 44% for phospholipid coating (NS). The ACT increased from 146 +/- 7 sec at 10 min to 159 +/- 16 sec after 6 hours for heparin, compared with 122 +/- 4 to 126 +/- 5 sec for phospholipid (p < 0.05). Thrombin time changed from 18 +/- 0 sec before to 19 +/- 1 sec after 6 hours for heparin, as compared with 16 +/- 1 sec to 18 +/- 1 sec for phospholipid (NS). Factor I levels decreased from 1.5 +/- 0.3 g/L to 1.3 +/- 0.1 g/L for heparin, compared with 1.5 +/- 0.2 g/L to 1.4 +/- 0.3 g/L for phospholipid. Antithrombin III levels changed from 102 +/- 26% to 91 +/- 7% for heparin, compared with 123 +/- 12% to 118 +/- 12% for phospholipid. Fibrinopeptide A levels changed from 100 +/- 60% to 130 +/- 13% for heparin, compared with 100 +/- 11% to 99 +/- 6% for phospholipid (P < 0.05). No macroscopic red clots were found in either group.(ABSTRACT TRUNCATED AT 250 WORDS)