Red blood cell transfusions are an extremely common medical intervention in both the United States and worldwide; over 14 million units of blood are transfused in the United States. Between 60 and 70 percent of all blood is transfused in the surgical setting. Despite the common use of red blood cell transfusions, the threshold for transfusion has not been adequately evaluated and is very controversial. A decade ago, the standard of care was to administer a peri-operative transfusion whenever the hemoglobin (Hgb) level fell below 10 g/dl (the "10/30 rule"). Concerns about the safety of blood, especially with respect to HIV and hepatitis, and the absence of data to support a 10 g/dl threshold led to the current standard of care, which is to administer blood transfusions based on the presence of symptoms, and not a specific Hgb/hematocrit level. However, there have not been any randomized clinical trials done with surgical patients that have tested the efficacy and safety of withholding blood until the patient develops symptoms, or the "10/30" approach to transfusion. Patients with underlying cardiovascular disease are at greatest risk of adverse effects from reduced Hgb levels.