The Multicenter Automatic Defibrillator Implantation Trial(MADIT)-II demonstrated that implantable cardioverter defibrillators(ICDs) save lives when used in patients with a history of myocardial infarction(MI) and an ejection fraction of 0.3 or less. Abstract: To investigate the cost-effectiveness of implanting ICDs in patients who met MADIT-II eligibility criteria and were enrolled in the Duke Cardiovascular Database between 1 January 1986 and 31 December 2001. Design: Cost-effectiveness analysis. Data Sources: Published literature, databases owned by Duke University Medical Center, and Medicare data. Target Population: Adults with a history of MI and an ejection fraction of 0.3 or less. Time Horizon: Lifetime. Perspective: Societal. Interventions: ICD therapy versus conventional medical therapy. Outcomes Measures: Cost per life-year gained and incremental cost-effectiveness. Results: Compared with conventional medical therapy, ICDs are projected to result in an increase of 1.80 discounted years in life expectancy and an incremental cost-effectiveness ratio of ＄ 50 500 per life-year gained. Cost-effectiveness varied dramatically with changes in time horizon: The cost-effectiveness ratio increased to ＄ 67 800 per life-year gained, ＄ 79 900 per life-year gained, ＄ 100 000 per life-year gained, ＄ 167 900 per life-year gained, and ＄ 367 200 per life-year gained for 15- year, 12- year, 9- year, 6- year, and 3- year time horizons, respectively. Changing the frequency of follow-up visits, complication rates, and battery replacements had less of an effect on the cost-effectiveness ratios than reducing the cost of ICD placement and leads. Limitations: The study was limited by the completeness of the data, referral bias, difference in medical therapy between the Duke cohort and the MADIT-II cohort, and not addressing potential upgrades to biventricular devices. Conclusions: The economic expense of defibrillator implantation in all patients who meet MADIT-II eligibility criteria is substantial. However, in the range of survival benefit observed in MADIT-II, ICD therapy for these patients is economically attractive by conventional standards. The Multicenter Automatic Defibrillator Implantation Trial (MADIT) -II demonstrated that implantable cardioverter defibrillators (ICDs) save lives when used in patients with a history of myocardial infarction (MI) and an ejection fraction of 0.3 or less. Abstract: To investigate the cost- effectiveness of implanting ICDs in patients who met MADIT-II eligibility criteria and were enrolled in the Duke Cardiovascular Database between 1 January 1986 and 31 December 2001. Design: Cost-effectiveness analysis. Data Sources: Published literature, databases owned by Duke University Medical Center Target Population: Adults with a history of MI and an ejection fraction of 0.3 or less. Time Horizon: Lifetime. Perspective: Societal. Interventions: ICD therapy versus conventional medical therapy. Outcomes Measures: Cost per life-year and incremental cost-effectiveness. Results: Compared with conventional medical therapy, ICDs are projected to result in an increase of 1.80 disco unted years in life expectancy and an incremental cost-effectiveness ratio of $ 50 500 per life-year gained. Cost-effectiveness varied dramatically with changes in time horizon: The cost-effectiveness ratio increased to $ 67 800 per life-year gained, $ $ 900 000 per life-year gained, $ 167 900 per life-year gained, and $ 367 200 per life-year gained for 15- year, 12- year, 9- year, 6- year, and 3-year time horizons, respectively. Changing the frequency of follow-up visits, complication rates, and battery replacements had less of an effect on the cost-effective ratios than reducing the cost of ICD placement and leads. Limitations: The study was limited by the completeness of the data, referral bias, difference in medical therapy between the Duke cohort and the MADIT-II cohort, and not not addressing potential upgrades to biventricular devices. Conclusions: The economic expense of defibrillator implantation in all patients who meet MADIT-II eligi bility criteHowever, in the range of survival benefit observed in MADIT-II, ICD therapy for these patients is economically attractive by conventional standards.