The objective of the study is to confirm the safety and efficacy of the BIOMONITOR III system. Furthermore, the insertion procedure, the use and handling of the incision and insertion tools and the sensing quality of the BIOMONITOR III will be assessed.

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 study and has provided written informed consent.
• Patient is willing and able to perform all follow up visits at the study site.
• Patient is willing and able to use the CardioMessenger and accepts the BIOTRONIK Home Monitoring concept.

Exclusion Criteria:

• Patients implanted with ICD or pacemaker.
• Patient is pregnant or breast feeding.
• Patient is less than 18 years old.
• Patient is participating in another interventional clinical investigation
• Patient´s life-expectancy is less than 6 months.