Lee JH, Kim SH, Lee W, et al. - Researchers conducted this retrospective observational study to examine the long-term prognostic implications of transient new-onset atrial fibrillation (AF) in patients with acute myocardial infarction (AMI). The sample consisted of 2,523 patients who presented with AMI from June 3, 2003, to February 24, 2015, after the exclusion of those with prior AF or in-hospital death. According to the occurrence and type of new-onset AF, patients were divided into three groups: (a) sinus rhythm (SR) group; (b) paroxysmal AF (PaAF: AF converted to SR prior to discharge) group and (c) persistent AF (PeAF: AF persisted during the hospitalisation) group. According to results, new-onset AF has been observed in 271 patients. With poor long-term outcomes, new-onset AF following AMI is correlated. Particularly when AF episodes are brief and are converted to SR, an increased risk of recurrent AF and stroke remains associated with new-onset AF.