A young man with congenital heart disease (ostium primum defect and cleft mitral valve) and severe factor VIII deficiency developed increasing exercise intolerance despite digoxin therapy. Open heart surgery was done in April 1972. Levels of factor Vlll were maintained above 60% and no abnormal bleeding occurred during or following surgery. Although the infusion of factor VIII concentrates increased plasma fibrinogen concentration sevenfold, there was no plasma accumulation of fibrin split products and no significant alteration in platelet function was detected. The sole complication of replacement therapy was a mild hemolytic anemia, due to isohemagglutinin contamination of the factor VIII concentrate. The patient described is the second hemophiliac to undergo open heart surgery in the United States, and the first survivor.