# Apple Heart Study

Study · id `cardio:apple-heart-study` · Cardiovascular Atlas · release `f6f6f1b6f50379ed` (public)

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Also called: AHS

Browse, condition area: Heart rhythm problems  

## In plain language

A large US study of whether a smartwatch alert for an irregular pulse matches atrial fibrillation on an ECG. People with a compatible iPhone and Apple Watch who reported no atrial fibrillation joined through an app. Those who got an alert were offered a telemedicine visit and a mailed ECG patch. The study checked how often alerts matched the ECG. It did not test whether alerts prevent strokes.

## Technical summary

Single-group, siteless, pragmatic study (NCT03335800), sponsored by Apple Inc. with Stanford University as registry collaborator; the registry names two principal investigators, both at Stanford. The registry records an interventional study, phase not applicable, allocation not applicable, one arm, no masking and primary purpose screening. Enrollment differs by source: the registry gives 419927 (actual) and the abstract of the main paper says 419,297 participants were recruited. The sources do not explain the difference and it is not reconciled. The registry lists two primary outcomes (AF on ambulatory ECG among notified participants, and confirmed AF with a detection by an app component) and two secondary outcomes (concordance with the app algorithm notification, and self-reported contact with a health care provider). No findings are recorded as structured rows here; the results are in the claim for the technology.

## Key facts

- Design: Single-group, siteless, pragmatic study. The registry gives allocation not applicable, one arm, no masking and primary purpose screening. A smartwatch irregular-pulse notification algorithm flagged possible atrial fibrillation, which started a telemedicine visit and a mailed ECG patch to wear for up to 7 days (abstract).
- Phase: Not applicable
- Enrolled: 419927 participants (enrolled count; Apple Heart Study: Assessment of Wristwatch-Based Photoplethysmography to Identify Cardiac Arrhythmias, snapshot `cardio:ctgov-nct03335800-2026-10-14`, retrieved 2026-10-14); 419297 participants (enrolled count; Large-Scale Assessment of a Smartwatch to Identify Atrial Fibrillation, snapshot `cardio:pubmed-31722151-2026-10-14`, retrieved 2026-10-14)
- Started: 2017-11-29 (actual) (Apple Heart Study: Assessment of Wristwatch-Based Photoplethysmography to Identify Cardiac Arrhythmias, snapshot `cardio:ctgov-nct03335800-2026-10-14`, retrieved 2026-10-14)
- Primary completion: 2019-02-21 (actual) (Apple Heart Study: Assessment of Wristwatch-Based Photoplethysmography to Identify Cardiac Arrhythmias, snapshot `cardio:ctgov-nct03335800-2026-10-14`, retrieved 2026-10-14)
- Completion: 2019-02-21 (actual) (Apple Heart Study: Assessment of Wristwatch-Based Photoplethysmography to Identify Cardiac Arrhythmias, snapshot `cardio:ctgov-nct03335800-2026-10-14`, retrieved 2026-10-14)
- Results first posted: 2020-03-30 (Apple Heart Study: Assessment of Wristwatch-Based Photoplethysmography to Identify Cardiac Arrhythmias, snapshot `cardio:ctgov-nct03335800-2026-10-14`, retrieved 2026-10-14)
- Countries: United States (Apple Heart Study: Assessment of Wristwatch-Based Photoplethysmography to Identify Cardiac Arrhythmias, snapshot `cardio:ctgov-nct03335800-2026-10-14`, retrieved 2026-10-14)
- Care setting: Remote and siteless. Participants consented through a smartphone app and no on-site visits were required. After an alert, follow-up used a telemedicine visit and a mailed ECG patch. (Large-Scale Assessment of a Smartwatch to Identify Atrial Fibrillation, snapshot `cardio:pubmed-31722151-2026-10-14`, retrieved 2026-10-14)
- Registry status: "COMPLETED" (U.S. National Library of Medicine (ClinicalTrials.gov), snapshot `cardio:ctgov-nct03335800-2026-10-14`, retrieved 2026-10-14)

## Connected pages

- Tests wristwatch-based photoplethysmography to identify arrhythmias: Smartwatch irregular-pulse detection (`cardio:wearable-rhythm-detection`)
- Lists atrial fibrillation as its first condition: Atrial fibrillation (AF) (`cardio:atrial-fibrillation`)
- Lead sponsor: Apple (`cardio:apple`)
- Main results, NEJM 2019: Apple Heart Study results, NEJM 2019 (`cardio:pub-apple-heart-study-nejm-2019`)

## Provenance

Content hash: dbbab2122db325106ec439de370a090ed2c266b98e7e68f9125485ff25d59d62
Last substantive edit: 2026-10-15
Evidence last checked: 2026-10-14