BACKGROUND: Clinical trials have shown that implantable cardioverter defibrillators (ICDs) improve survival in patients with sustained ventricular arrhythmias. OBJECTIVE: To determine the efficacy necessary to make prophylactic ICD or amiodarone therapy cost-effective in patients with myocardial infarction. DESIGN: Markov model-based cost utility analysis. DATA SOURCES: Survival, cardiac death, and inpatient costs were estimated on the basis of the Myocardial Infarction Triage and Intervention registry. Other data were derived from the literature. TARGET POPULATION: Patients with past myocardial infarction who did not have sustained ventricular arrhythmia. TIME HORIZON: Lifetime. PERSPECTIVE: Societal. INTERVENTIONS: ICD or amiodarone compared with no treatment. OUTCOME MEASURES: Life-years, quality-adjusted life-years (QALYs), costs, number needed to treat, and incremental cost-effectiveness. RESULTS OF BASE-CASE ANALYSIS: Compared with no treatment, ICD use led to the greatest QALYs and the highest expenditures. Amiodarone use resulted in intermediate QALYs and costs. To obtain acceptable cost-effectiveness thresholds (