Open chest cardiopulmonary bypass was evaluated in eight canine experiments (mean bodyweight 37 +/- 7 kg) over 24 hours using either heparin surface coated equipment without systemic anticoagulation or standard equipment with systemic heparinization (ACT greater than 400 s). Mean duration of perfusion achieved was 23 +/- 2 hours in the group perfused without systemic anticoagulation versus 21 +/- 6 hours in the group with: [table; see text] These results show, that prolonged open chest perfusion by the means of heparin surface coated equipment without systemic anticoagulation can be performed with reduced blood trauma and without transfusion of blood products for 12 hours.