“…1 This can usually be achieved using iv heparin doses of 300-400 IU·kg -1 . However, considerable variability in the response to heparin is frequently observed, with some patients requiring much higher doses to achieve the target ACT, a condition known as heparin resistance, [2][3][4] or altered heparin responsiveness. 5 Some preexisting conditions described to be associated with heparin resistance during cardiac surgery are infection, 6,7 use of an intra-aortic balloon pump (IABP), 4 and, most frequently, preoperative therapy with heparin infusion.…”