OBJECTIVES: Patients presenting to hospital with acute, undifferentiated chest pain have a low, but important, risk of significant myocardial ischaemia. Potential diagnostic strategies for patients with acute, undifferentiated chest pain vary from low cost, poor effectiveness (discharging all home) to high cost, high effectiveness (admission and intensive investigation). This paper aimed to estimate the relative cost effectiveness of these strategies. METHODS: Decision analysis modelling was used to measure the incremental cost per quality adjusted year of life (QALY) gained for five potential strategies to diagnose acute undifferentiated chest pain, compared with the next most effective strategy, or a baseline strategy of discharging all patients home without further testing. RESULTS: Cardiac enzyme testing alone costs pound 17 432/QALY compared with discharge without testing. Adding two to six hours of observation and repeat enzyme testing costs an additional pound 18 567/QALY. Adding exercise testing to this strategy costs pound 28 553/QALY. A strategy of overnight admission, enzyme, and exercise testing has an incremental cost of pound 120 369/QALY, while a strategy consisting of overnight admission without exercise testing is subject to extended dominance. Sensitivity analysis revealed that the results are sensitive to variations in the direct costs of running each strategy and to variation in assumptions regarding the effect of diagnostic testing upon quality of life of those with non-cardiac disease. CONCLUSION: Observation based strategies incur similar costs per QALY to presently funded interventions for coronary heart disease, while strategies requiring hospital admission may be prohibitively poor value for money. Validation of the true costs and effects of observation based strategies is essential before widespread implementation.