Aims Mitral regurgitation(MR) following an acute myocardial infarction(AMI) confers an adverse prognosis during long term follow- up. There are no studies evaluating the influence of pre- AMI MR in the short- and long- term prognosis of such patients. Our aim was to assess the prognostic value of pre- AMI MR in the short and long- term follow- up of patients who suffered a first AMI and to assess its influence on left ventricular haemodynamics. Methods and results Sixty- eight consecutive patients with a first AMI and an echocardiographic study before AMI(< 3 months) were included in the study. The pre- AMI echo was performed for various reasons. Of these 68 patients, 42 had pre- AMI MR(Group 1) and 26 showed no pre- AMI MR(Group 2). The presence of degenerative changes at the level of the mitral valve was confirmed in all cases. Patients with any other cause of MR were excluded. Clinical and echocardiographic variables for both phases(pre- AMI and post- AMI) were analysed and patients were followed up. Mean age was 75.5± 9.5 years; there were 38 males(55.9% ). There were no statistical differences in baseline clinical variables between the groups, except for the presence of pre- AMI atrial fibrillation, which was more frequent in Group 1(21.4 vs. 0% ; P=0.01 ). After AMI, only end- diastolic left ventricular diameter was significantly larger in Group 1(54.9± 4.7 vs. 48.1± 5.6 mm; P< 0.001). During long- term follow- up, median survival times were 912 days(interquartile range: 690 days) in Group 1 and 1423 days(interquartile range: 520 days) in Group 2(Log- rank P=0.02). The multi- variable analysis showed that the presence of pre- AMI MR relates to a statistically significant relationship with a worse post- AMI evolution[relative risk(95% confidence interval): 3.8(1.1- 13.1); P=0.037]. Conclusion The present study shows that the presence of pre- AMI MR is an independent prognostic marker among those patients suffering a first AMI.