Methods: The NOR-FIB study is a multi-centre prospective observational trial, designed to evaluate detection of AF in cryptogenic stroke and transient ischemic attack (TIA). Patients admitted with cryptogenic stroke or TIA in stroke units in the Nordic countries, aged 18-80 years are included and have the Reveal LINQ® Insertable cardiac monitor system implanted for 12 months for the purpose of AF detection. Biomarkers that may identify patients, who could derive the most clinical benefit from the detection of AF by prolonged monitoring, are being studied.