In the United States there may be four to five million patients with silent myocardial ischemia, including approximately 50,000 asymptomatic patients who have had myocardial infarction, one to two million asymptomatic patients with no history of myocardial infarction or angina, and three million patients with angina. The prognosis for patients who have had infarction and for patients with angina varies, but, in general, it is worse for patients with more extensive disease because sudden cardiac death may be the only clinical sign in asymptomatic patients. Silent myocardial ischemia is an important public health issue; it is hoped that its detection may prevent many episodes of sudden cardiac death annually.