The Heparin Removal Device is a deheparinization system that provides a good alternative when adverse reaction to protamine is suspected or when a heparin coated device is employed for cardiopulmonary bypass. In a bovine model, after systemic heparinization with 300 IU/kg body wt, the authors investigated the rate of deheparinization using this plasmapheresis system that allows exposition of heparinized plasma to an immobilized cationic ligand. Blood was shunted through a heparin coated veno-venous circuit to the plasma separator at a flow rate of 500 ml/min (n = 3, body wt 68 +/- 4 kg) or 1,000 ml/min (n = 3, body wt 57 +/- 4 kg). All plasma separators remained patent without any failure of the devices. Blood samples were drawn at regular intervals for coagulation parameters. The evolution of the activated coagulation time (ACT) was measured during the first 60 min of the deheparinization procedure, and results were compared with spontaneous evolution in a control group (n = 3, body wt 73 +/- 5 kg) without reversal of heparinization. After heparin administration, mean ACT was longer than 1,000 sec in the three groups. Fifteen minutes later it was still > 1,000 sec in the control group, whereas it was 427 +/- 8 sec in the slow flow group (500 ml/min) and 340 +/- 26 sec in the high flow group (1,000 ml/min). At 30 min it was 1,000, 367 +/- 26, and 200 +/- 24 sec, respectively, in the three groups. A regression curve was calculated for each group, and areas under the curves were compared. Ex vivo deheparinization was efficient in normalization of ACT, but removal of heparin appeared to be flow rate dependent. Increased blood flow from 500 to 1,000 ml/min across the deheparinization system resulted in significant acceleration of ACT normalization (p < 0.05).