Heparin resistance (HR) is an increasingly common occurrence due to a greater awareness of the benefits of antithrombosis prophylaxis in hospitalised patients with low molecular weight and unfractionated heparin. Furthermore as more high-risk patients with prior heparin exposure undergo cardiac surgery we can expect to encounter more such cases. Adequate anticoagulation is essential for the safe conduct of any operation requiring cardiopulmonary bypass and is usually achieved with systemic heparinisation. We report a case of successful anticoagulation with the intraoperative administration of fresh frozen plasma in a high-risk coronary patient with HR and highlight the perils of unwitting overheparinisation in such cases. This case highlights the importance of clinical awareness of this phenomenon and the available alternative anticoagulants.