Cold agglutinins are autoantibodies activated at low temperature to produce red blood cell agglutination and hemolysis. Systemic hypothermia and cold cardioplegia which are employed commonly in modern cardiac operations are a potential danger to patients with the cold agglutinin disease. We report a successful use of a continuous warm retrograde delivery of cardioplegia with systemic hypothemia in a patient with cold agglutinin disease detected incidentally. Hemagglutination was found in the cold (4oC) blood cardioplegic circuit before the delivery of the cardioplegic solution. Hemagglutination was not detected in the mixture of blood and the warm cardioplegic solution (36.5oC). Therefore, cold agglutinin disease was suspected. The patient was only mildly cooled systemically. The coronary system was perfused with a normothemic cardioplegic solution. With this technique, the patient underwent an uneventful mitral valve replacement operation.