Two patients--one an infant and the other an adolescent--with transposition of the great arteries and hemophilia underwent a successful major reconstructive open-heart surgical procedure. Despite a severe coagulation deficiency, a major reconstructive cardiac operation was performed with the use of a detailed replacement plan, which took into consideration the potency of the replacement material and its potential hazards, biologic half-life, and anticipated in vivo recovery on the basis of the patient's plasma volume. To our knowledge, these are the first reports of successful surgical repair of this type in patients with severe coagulation factor deficiency.