A 83-year-old man was admitted because of heart failure due to severe aortic stenosis and mitral regurgitation secondary to chordal rupture of the anterior leaflet. Mild anemia and elevated serum lactate dehydrogenase were present with reticulocytosis and haptoglobinemia. Direct Coombs test was positive. Coexistence of autoimmune hemolytic anemia was identified, but the main cause of his hemolysis was thought to be mechanical hemolysis due to stenotic valve and/or ruptured chordae because of the presence of red cell fragmentation. The patient successfully underwent double valve replacement. Improvement of anemia was coupled with reduction of the serum lactate dehydrogenase level. Valvular shear stress on the red cells and reduction of red cell deformability secondary to autoimmune hemolytic anemia were thought to be responsible for his hemolysis.