Patients with underlying serious hea disease need to have their hemoglobin level kept above:

Patients without serious underlying cardiovascular or pulmonary disease can tolerate hemoglobin levels above 8 g/dL; Patients with serious underlying cardiovascular or pulmonary disease need to have their hemoglobin levels kept above 11 g/dL. Reference: Harrisons Principles of Internal Medicine, 18th Edition, Page 851