The Framingham study demonstrated that 25% of all episodes of acute myocardial infarction (AMI) do not present clinical symptoms, and are later recognized in a routine ECG. Silent ischaemia is frequently found after acute myocardial infarction, and has been identified in 25-60% of the patients according to the results of different studies and the different criteria employed for diagnosis. Silent ischaemia after AMI, as well as angina, is related with the presence and extent of severe coronary lesions located in the infarct related coronary artery or in other vessel not responsible for the acute episode of necrosis. The prognostic significance of silent ischaemia after AMI has not been well established. In some studies the painless ST segment depression during an exercise test soon after AMI presented the same prognostic value that the ST segment depression accompanied by angina, but in others the symptomatic episodes were a better predictor of major events and long term survival after the infarct. Several studies employing ambulatory ECG monitoring (Holter) also seem to indicate that the painless and transient episodes of ST segment depression identify a group of patients with worse prognosis, but in these studies the patients were selected, introducing a clear bias in the results of these investigations. Finally, asymptomatic transient perfusion defects in thallium studies clearly identify a group of high risk patients with a higher incidence of complications and higher mortality rate than the patients with negative thallium studies. The efficacy of anti-ischaemic drugs or myocardium revascularization procedures, including surgery, has not been studied in patients with silent ischaemia after acute myocardial infarction.(ABSTRACT TRUNCATED AT 250 WORDS)