Background. Re-exploration for bleeding after cardiac surgery is an indicator of substantial haemorrhage and is associated with increased hospital resource utilization. This study aimed to analyse the costs of re-exploration and estimate the costs of haemostatic prophylaxis. less thanbrgreater than less thanbrgreater thanMethods. A total of 4232 patients underwent isolated, first-time, coronary artery bypass graft (CABG) surgery during 2005-8. Each patient re-explored for bleeding (n = 127) was matched with two controls not requiring re-exploration (n = 254). Cost analysis was based on resource utilization from completion of CABG until discharge. A mean cost per patient for re-exploration was calculated. Based on this, the net cost of prophylactic treatment with haemostatic drugs for preventing re-exploration was calculated. less thanbrgreater than less thanbrgreater thanResults. Patients undergoing re-exploration had higher exposure to clopidogrel before operation, prolonged stays in the intensive care unit, and more blood transfusions than controls. The mean incremental cost for re-exploration was (sic)6290 [95% confidence interval (CI) (sic)3408-(sic)9173] per patient, of which 48% [(sic)3001 (95% CI (sic)249-(sic)2147)] was due to prolonged stay, 31% [(sic)1928 (95% CI (sic)1710-(sic)2147)] to the cost of surgery/anaesthesia, 20% [(sic)1261 (95% CI (sic)1145-(sic)1378)] to the increased number of blood transfusions, and andlt;2% [(sic)100 (95% CI (sic)39-(sic)161)] to the cost of haemostatic drugs. A cost model, at an estimated 50% efficacy for recombinant activated clotting factor VIIa and a 50% expected risk for re-exploration without prophylaxis, demonstrated that to be cost neutral, prophylaxis of four patients needed to result in one avoided re-exploration. less thanbrgreater than less thanbrgreater thanConclusions. The resource utilization costs were substantially higher in patients requiring re-exploration for bleeding. From a strict cost-effectiveness perspective, clinical interventions to prevent haemorrhage might be underutilized.