Exercise Testing, whether it is convention exercise electrocardiography or exercise imaging with perfusion scintigraphy or echocardiography, has many purposes. Its best-know application is to diagnose coronary artery disease, and in this role it serves as a model for reasoning about diagnostic tests. Among the other uses of exercise testing, including measuring exercise capacity, evaluating the efficacy of therapy, establishing an exercise prescription, and reassuring the patient about the safety of exercise, assessing prognosis is one of the most important, but it has been overshadowed by the emphasis on diagnosis.