The study includes collection of data from patients referred to a therapeutic evaluation in Tays Sydänkeskus Oy (Heart Center Co, Tampere University Hospital) or another unit of Sydänkeskus (hereafter the Heart Hospital) due to suspected cardiac arrhythmia. Data collection takes place outside the hospital in normal daily conditions. The monitoring is started during the outpatient visit at Heart hospital polyclinic or when leaving home from cardiac ward and it continues for 2 days. Reference information about the occurrence of arrhythmia episodes and the reference ECG data are obtained from simultaneously worn Holter device.

During the two days the study device and the reference device are worn continuously. Wearing the devices does not affect the daily routines of the participant except there is no possibility to take a shower. The arrhythmia episodes are labelled in post-hoc signal analysis and annotations visually confirmed by a cardiologist. The participants are instructed to take ECG recordings with the wrist device every time the device gives a notification and also whenever the participant feels arrhythmia symptoms. There will be at least four intermittent ECG records taken on each day.

Inclusion Criteria:

• Age: ≥ 18 years
• Suspected or earlier diagnosed episodic cardiac arrhythmia, for example atrial fibrillation or atrial flutter
• Ability to give informed consent
• Volunteering for the study

Exclusion Criteria:

• Implanted permanent pacemaker
• Inability to give informed consent e.g. due to mental confusion
• Denial

The source population of the study includes patients referred to a therapeutic evaluation or treatment in Tays Heart Hospital due to suspected cardiac arrhythmia. A portion (up to one third) of the subjects may be having on-going atrial fibrillation at the beginning of the measurement and may suffer from persistent or permanent atrial fibrillation.