Background. The objectives of this study were to determine the hemoglobin transfusion thresholds, and the factors that influence physicians' decisions when transfusing coronary artery bypass surgery patients.Methods. We conducted a cross-sectional study using pilot tested, self-administered, mailed questionnaires sent to all anesthesiologists and cardiac surgeons in Canada participating in coronary bypass surgery.Results. The response rates for the intraoperative and postoperative questionnaires were 70.5% (345/489) and 60.7% (297/489), respectively. Responses were received from anesthesiologists from all cardiac centers and from cardiac surgeons from 30/32 cardiac centers. The mean hemoglobin concentrations for transfusion were 69 g/L and 72 g/L for the intraoperative and postoperative base case scenarios, respectively. Regression analysis identified the presence of myocardial ischemia, cardiac index and age as factors affecting the transfusion threshold intraoperatively and postoperatively (P < 0.0001).Conclusion. Future studies are required to elucidate whether transfusions based on these variables affect patient morbidity and mortality.