The extent of implementation in daily clinical practice of the new definition of myocardial infarction is unknown. The purpose of the present study was to describe the use of the new definition in patients discharged from a cardiology department. We analyzed the clinical records of 277 patients admitted because of acute coronary syndromes and discharged from the cardiology department between 1 March 2001 and 31 August 2001. The final clinical diagnosis based on the presence of classical or only new diagnostic criteria was studied. 127 patients (46%) satisfied the new definition (61% classical criteria and 39% only new criteria). Only 98 (77%) of the patients with myocardial infarction according to the new definition were discharged with this diagnosis (96% of the group that satisfied classical criteria and 48% of the group that satisfied only new criteria). The diagnosis of myocardial infarction is still based predominantly on classical criteria; the new criteria have been only partially implemented.