Silent (asymptomatic) myocardial ischemia (SMI) is defined as a transient alteration in myocardial perfusion in the absence of chest pain or the usual anginal equivalents. Patients may be classified as having one of the three types of SMI: type A--totally asymptomatic patients with no history of angina or myocardial infarction; type B--asymptomatic patients with previous myocardial infarction; type C--patients with angina and asymptomatic ischemic episodes. SMI has been found in 2.5% of all healthy males aged 40-59 and in 20% of all postinfarction patients. In type C-patients, 80% has been found to have asymptomatic ischemic episodes in addition to typical angina pectoris. The frequency of SMI may be up to three or four times that of anginal attacks. SMI patients have generally reduced sensitivity to pain an differences in severity an duration of ischemic episodes. Diagnosis is based on screening by means of exercise testing in patients working in specific professions (like pilots, busdrivers etc.), in postinfarction patients and in patients after unstable angina pectoris and after coronary bypass surgery or coronary angioplasty. Prognosis is the same as in asymptomatic ischemia. SMI is an indicator of instability in certain groups of patients (post infarction, after unstable angina pectoris). SMI persisting after medical therapy of unstable angina is associated with adverse short-term-prognosis, therefore coronary surgery or angioplasty is indicated.