Atrial fibrillation (AF) is themost common clinical arrhythmia, and increases risk of stroke 5-fold [1]. Approximately 1/6 strokes are AFrelated [2]. These cardio-embolic strokes are severe, and in 18% the underlying AF is previously undiagnosed [2] [3]. Although the occurrence of palpitations is often a guide to the presence of AF, and the symptomatic status of patients with known AF has been well described [3], the proportion of subjects with incidentally discovered AF who do not have palpitations and are therefore unlikely to present to a physician has not previously been reported. The resulting societal burden of the largely preventable strokes in unrecognized AF could be substantially reduced by screening programs to detect incidental AF and initiating appropriate thrombo-prophylaxis with oral anticoagulants (OAC). To establish whether screening for AF may be warranted, we studied an ambulatory pre-operative population, the majority of whom were scheduled for a minor procedure, to determine the prevalence of incidental AF and the symptomatic status of those with this previously undiagnosed arrhythmia. These relatively healthy ambulant subjects should be representative of the general community.Wewere particularly interested in the prevalence of asymptomatic AF in subjects aged≥65, as such individualswould be unlikely to present to a physician andwould be most likely to benefit from thrombo-prophylaxis. A routine ECG is performed in every ambulatory subject aged ≥40 years prior to elective surgery at our Hospital. All pre-admission ECGs between January–August 2011 were reviewed: charts of those in AF were examined and validated through contact with their primary care physician to determinewhether AFwas previously diagnosed or an incidental finding. We also examined pre-procedural questionnaires administered prior to the ECG, to determine symptom status, and collected demographics, co-morbidities, medications, and calculated CHADS2/CHA2DS2VASc scores [4,5]. The authors of this manuscript have certified that they comply with the Principles of Ethical Publishing in the International Journal of Cardiology. Of2802ECGs reviewed,112 (4%) showedAF, and in12of these (0.4%) AF was an incidental finding. In those ≥65 years the prevalence of AF rose to 6.7% and was incidental in 0.7% (10/1459) (Table 1). The mean age of subjects with incidental AF was 71±9 and did not differ from those with known AF. All with incidental AF were male, compared to 70% with known AF (pb0.05). Only 20% of those aged≥65with incidental AF reportedpalpitations. Thisfindingmaybe explained bya relatively lowmean restingheart rate (78±14), which was virtually identical to that seen in known AF (77 ±16), despite absence of rate-controlling medication in subjects with incidental AF. Mean CHADS2/CHA2DS2VASc scores were slightly higher in thosewith known compared to incidental AF in the overall group and in those ≥65, but differences were not significant. Mean CHADS2 score in those with incidental AF aged ≥65 was 2.2±1.5, and 7/10 had CHADS2≥2. Mean CHA2DS2VASc score in those with incidental AF≥65 was 3.8±2.0 (Fig. 1). OAC were prescribed in only 65% of patients with known AF and CHADS2≥2, consistent with the known evidence– practice gap (Table 1). Our screening of an otherwise relatively healthy ambulant population≥65 scheduled for elective predominantly minor surgery found a prevalence of 0.7% undiagnosed AF. This figure is likely an underestimate of the prevalence, and would be higher with periodic screening as a single ECG cannot detect all with paroxysmal AF. Most importantly, very few subjects reported palpitations, which is not surprising, as the resting heart was not elevated. The mean heart rate was relatively low even though no subject received heart rate slowing medications and may explain why such subjects are unlikely to present with symptoms of AF until sequelae like stroke or other thrombo-embolic manifestations occur. Understanding this phenomenon should motivate physicians to screen for AF at regular intervals, rather than wait for symptoms to occur, especially in those aged ≥65. Pulse palpation followed by a confirmatory ECG is simple, quick and may be of similar efficacy to routine ECG screening for detection of new AF in patients≥65 in general practice [6]. However, not all those with silent AF regularly visit their doctor, especially if asymptomatic, which makes a community ECG or pulse screening program potentially attractive if we are to make an impact