OBJECTIVES: This research uses a Markov model of acute coronary syndrome (ACS) to determine the magnitudes of cost drivers affected by new treatments. METHODS: A Markov model was built using TreeAge Pro Healthcare and parameterized to replicate the Clopidogrel in Unstable angina to prevent Recurrent ischemic Events (CURE) trial. The model reports results at 30 days, then every six-months over three-years for clopidogrel plus aspirin vs. a hypothetical alternative. Reductions in risk for five events are analyzed: myocardial infarction (MI), initial and subsequent percutaneous coronary intervention (PCI), refractory ischemia, and stroke. Modeled risks and costs of coronary bypass surgery and bleeding complication are not modified. Resulting states include: no event, post each event type, various cardiac deaths, and non-cardiac death. RESULTS: The effects on costs of reducing relative risks of each event (and all five together) by 10% and 20% are evaluated. Cost offsets at one and three-years are highest for initial PCI ($239, $724; 2.0%, 2.8% of total costs for time period) for a 20% six-month risk reduction. All other one-year offsets are less than 1.0%. Ten percent reductions produce nearly half the cost savings. Total savings for a 20% reduction in all five events are ($493, $1530; 4.1%, 5.8%) at one and three-years. If, instead of reducing risks after the initial 30-day period, a 20% reduction in 30-day risk of PTCA is modeled, then costs decrease by $389, $480, and $616 at 30 days, one and three-years, respectively. CONCLUSIONS: In this model, initial PCI influences cost more than MI, refractory ischemia, subsequent PCI, or stroke, but all are clinically important. Knowing the relationship between event costs and risk reductions can help estimate the potential cost impact of new treatments.