AimsPatients with asymptomatic and undiagnosed atrial fibrillation (AF) are at increased risk of heart failure and ischaemic stroke. In this study, we validated a new diagnostic device, the MyDiagnostick, for detection of AF by general practitioners and patients. It records and stores a Lead I electrocardiogram (ECG) which is automatically analysed for the presence of AF.Methods and resultsIn total, 192 patients (age 69.4 ± 12.6 years) were asked to hold the MyDiagnostick for 1 min, immediately before a routine 12-lead ECG was recorded. Atrial fibrillation detection and ECGs stored by the MyDiagnostick were compared with the cardiac rhythm on the 12-lead ECG. In a second part of the study, the MyDiagnostick was used to screen for AF during influenza vaccination in the general practitioner's office. Atrial fibrillation was present in 53 out of the 192 patients (27.6%). All AF patients were correctly detected by the MyDiagnostick (sensitivity 100%; 95% confidence interval 93–100%). MyDiagnostick AF classification in 6 out of 139 patients in sinus rhythm was considered false positive (specificity 95.9%; 95% confidence interval 91.3–98.1%). During 4 h of influenza vaccination in 676 patients (age 74 ± 7.1 years), the MyDiagnostick correctly diagnosed AF in all 55 patients (prevalence 8.1%). In 11 patients (1.6%), AF was not diagnosed before, all with a CHA2DS2VASc score of >1.ConclusionThe high AF detection performance of the MyDiagnostick, combined with the ease of use of the device, enables large screening programmes for detection of undiagnosed AF.