Cold agglutinin disease is a type of autoimmune haemolytic anaemia caused by autoantibodies that bind to red blood cell antigens at a cold temperature and causes extravascular haemolysis and sometimes thrombosis also. Due to exposure to a lower temperature during open-heart surgery, the activation of haemolysis may occur in the presence of cold agglutinin antibodies. We present the management of a cyanotic child who has undergone open-heart surgery after the detection of high cold agglutinin titres during routine pre-transfusion screening.