Atrial fibrillation (AF), the most commonly encountered clinical arrhythmia, often complicates acute myocardial infarction (AMI) with an incidence between 6 and 21%. Predictors of the arrhythmia in the setting of AMI include advanced age, heart failure symptoms, and depressed left ventricular function. The bulk of evidence demonstrates that AF in patients hospitalized for AMI has serious adverse prognostic implications regarding in-hospital, but also long-term mortality. This seems to apply for all patient populations studied without significant differences related to the treatment of AMI (i.e. no reperfusion therapy vs. thrombolysis vs. percutaneous coronary intervention). Mortality is particularly high in patients who have congestive heart failure and/or a reduced left ventricular ejection fraction. Finally, there are persuasive data indicating that AF complicating AMI not only increases the risk for ischaemic stroke during hospitalization but also during follow-up. This seems to apply also for transient AF which has reversed back to sinus rhythm at the time of discharge. These observations emphasize the need for prospective studies evaluating optimal therapeutic approaches for patients with AMI complicated by AF.