Hospitalizations for patients with prosthetic heart valves undergoing noncardiac surgery are frequently prolonged for intravenous heparin therapy to decrease the incidence of thromboembolism while patients are not taking oral anticoagulant agents. Because the rate of thromboembolic events is quite low and the period of increased risk is very short, the cost of preventing these rare events can be great. We performed cost-effectiveness analyses addressing these issues. We calculated the marginal cost per additional quality-adjusted year of life gained per thromboembolic event averted and per death averted. We conclude that the marginal cost of prolonging hospitalization to administer heparin is prohibitively high compared with most contemporary therapies, except when the patient has the most thrombogenic of valves. We also discuss the ethical and legal ramifications of integrating the results of cost-effectiveness analyses into clinical practice.