This post-marketing study is conducted to characterize the ability of Apple Watch rhythm analysis software to identify Atrial Fibrillation (AF) and facilitate subsequent clinical evaluation among users who contact AppleCare.

Inclusion Criteria:

1. Possession of the following at time of eligibility screening:

   • iPhone (5s or later) with iOS version 12.1.1 or later defined as iPhone model/iOS version used to complete screening eligibility.
   • Apple Watch (Series 1-4) with watchOS version 5.1.2 or later defined as Apple Watch model/watchOS paired with iPhone used to complete screening eligibility

2. At least one of the following by self-report before consent:

   • Irregular Rhythm Notification
   • ECG app classification of Atrial Fibrillation
   • ECG app classification of Inconclusive defined as "Inconclusive," "Heart Rate Over 120," or "Heart Rate Under 50"

3. Age ≥ 22 years at time of eligibility screening

4. Current resident of the United States at time of eligibility screening, and will reside in the United States for the length of the study

5. Proficient in written and spoken English

6. Valid phone number associated with iPhone, ascertained from self-report

7. Valid email address, ascertained from self-report

Exclusion Criteria:

1. Shared iCloud account
2. Shared AppleWatch

9 months (participants may have reported adverse events at any time from enrollment to close of study)

The small number of enrolled participants prevents us from drawing meaningful conclusions from this study.