This study is a prospective, observational, multicenter international post-market study. The results of this study will describe the different patient groups for which the Reveal XT is being used for the diagnosis and monitoring of various cardiac arrhythmias. This study will also collect data regarding the clinical consequences of using the Reveal XT and the influence of Reveal XT data on clinical care pathways. The physician as well as the patient's satisfaction with the device will be evaluated. The study will be conducted in 60-100 centers primarily in Europe. It is expected that 800-1000 patients will be enrolled.