Hereditary spherocytosis is a clinically heterogeneous, genetically determined red blood cell membrane disorder resulting in hemolytic anemia. Structural or functional disorders of the cytoskeletal proteins result in the formation of spherocytes, which lack the strength, durability, and flexibility to withstand the stresses of the circulation. This problem can be accentuated by the deleterious effects of the heart-lung machine. Three patients with hereditary spherocytosis underwent open heart operation with no deaths and no serious complications resulting from the hematologic defect. Splenectomy is recommended, although not essential, before a cardiac operation, and mechanical valves should perhaps be avoided.