Master Study of the BIOMONITOR III and Incision and Insertion Tool (FIT OneStep)

Inclusion Criteria: * Patient is at high risk of developing a clinically important cardiac arrhythmia; or * Patient is undergoing investigation for symptoms such as palpitations, pre- syncope or syncope, that are suggestive of an underlying cardiac arrhythmia; or * Patient is undergoing investigation for the detection of atrial fibrillation following cryptogenic stroke; or * Patient is planned for AF ablative procedure or has already undergone an AF ablative procedure. * Patient is able to understand the nature of the study and able to provide written informed consent. * Patient is willing and able to perform all follow-up visits at the investigational site. * Patient is willing and able to use the CardioMessenger and accepts the BIOTRONIK Home Monitoring concept. Exclusion Criteria: * Patient is implanted with an ICD or pacemaker. * Patient is pregnant or breast-feeding. * Patient is less than 18 years old. * Patient's life-expectancy is less than 12 months. * Patient is participating in another interventional clinical investigation.