Anemia is an common condition in patients undergoing cardiac surgery, and it is often present in one quarter to half of patients at admission. Several studies have indicated that anemia is a major risk factor for worse outcomes, including increased risk of mortality and major morbidity and prolonged hospitalization. Anemia is a leading reason for use of allogeneic blood transfusions. Harmful effects of anemia are often attributed to the reduced oxygen carrying capacity of blood, reduced viscosity and the resulting impaired rheologic characteristics of blood, underlying comorbidities, and the side effects of treatments given for anemia, namely, allogeneic blood transfusions. Patients undergoing cardiac surgery may be at increased risk of anemia given the often-existing cardiac comorbidities and the negative impacts of cardiopulmonary bypass. However, whether less restrictive transfusion practices are justified in patients undergoing cardiac surgery is still a matter of debate. The prevalence of anemia often increases during hospital stay, and it can persist for a long time beyond hospital discharge. Given the associated risks and available management strategies, clinicians should remain vigilant to detect and treat anemia throughout the course of care for patients undergoing cardiac surgery.