Samsung Galaxy Watches can flag patterns suggestive of atrial fibrillation (AFib) and record a useful single-lead ECG, but they do not diagnose AFib or rule it out. The passive Irregular Heart Rhythm Notification (IHRN) and the user-initiated ECG measure different signals and have very different validation results. A watch alert deserves clinical follow-up; a normal reading is only a short snapshot.
The two Samsung features that look for AFib
| Feature | What it measures | How it works | Main limitation |
|---|---|---|---|
| IHRN | Intermittent optical pulse data (photoplethysmography) | Checks for an irregular pulse while you are relatively still, then can prompt an ECG | Not continuous; Samsung says it may miss episodes and does not notify for episodes shorter than one hour |
| On-demand ECG | Electrical activity from a single lead | You sit still and touch the watch electrode with the opposite hand for about 30 seconds | Needs a usable recording and is not equivalent to a clinical 12-lead ECG |
| IHRN followed by ECG | Two-stage pulse-screening and ECG workflow | An alert leads you to make a user-initiated recording | If IHRN misses the episode, the second step never occurs |
IHRN is pulse-irregularity screening, not an ECG. The ECG app records electrical activity, but Samsung describes it as an informational aid rather than a diagnosis. See Samsung’s feature description (Samsung Health Monitor) and the FDA filing (K240909).
Samsung’s official U.S. accuracy figures
The current U.S. Instructions for Use report separate results for separate tasks. The study used different participants and endpoints, so the percentages must not be combined into one “Samsung accuracy” number.
On-demand ECG
In a validation of 544 people aged 22 or older, a board-certified cardiologist classified a 12-lead ECG as the reference standard. Among recordings the watch could classify, Samsung reports 98.1% sensitivity (207 of 211 AFib subjects detected) and 100% specificity (223 of 223 sinus-rhythm subjects classified correctly). These figures are for classifiable recordings, not every attempted recording. Source: Samsung U.S. Instructions for Use.
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IHRN
A separate study enrolled 810 people aged 22 or older who wore a Galaxy Watch and ECG reference patch for up to 10 days. The target was a continuous AFib episode lasting at least one hour. IHRN sensitivity was 68.0% (102 of 150 participants with the target episode notified) and specificity was 98.8% (652 of 660 participants without a concordant episode not notified). This is not a universal real-world sensitivity for every AFib episode.
The sequential pathway
For the studied pathway in which an IHRN alert was followed by an ECG, Samsung reports 66.7% sensitivity and 100% specificity. Because this is a two-stage process, a missed passive alert prevents the confirmatory recording.
What sensitivity and specificity mean
- Sensitivity is the proportion of people who truly had the target rhythm, under the study conditions, whom the device identified.
- Specificity is the proportion of people without the target rhythm whom the device correctly left unflagged.
Neither value is the probability that your individual alert is true. That probability also depends on your underlying risk and how common AFib is in the population being tested.
Why ECG and IHRN percentages differ
An ECG is deliberately recorded when you choose the moment, remain still, maintain skin contact and complete the full recording. IHRN works opportunistically from intermittent optical checks while you are still and requires a persistent pattern. It can miss short, intermittent or poorly sampled episodes. The different sensors, user actions, episode definitions and reference standards make a lower IHRN sensitivity expected; it does not mean the ECG percentage applies to passive monitoring.
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What independent studies show
Samsung’s sponsored validation is not the whole evidence base. Results vary substantially with device generation, algorithm, population and handling of uninterpretable strips.
- The 2023 BASEL Wearable Study reported, for a Galaxy Watch 3 under its protocol, 85% sensitivity, 75% specificity and 17% inconclusive tracings. It should not be treated as a result for every newer Galaxy Watch or for current IHRN. Study record
- A 2025 review of 26 studies and 17,349 patients pooled Samsung-device estimates at approximately 97% sensitivity and 96% specificity, with substantial heterogeneity. That is research context, not a model-specific guarantee. Abstract and full text
- Another 2025 smartwatch-ECG review found pooled algorithmic-reading sensitivity of 86% and specificity of 94%. Review
Studies can disagree because they use different Galaxy generations and software, AFib definitions, reference tests, patient groups, episode patterns, recording conditions and calculations (per recording, episode or participant). Some exclude inconclusive readings; others count them, which can materially reduce apparent performance.
How to obtain the best Samsung ECG recording
- Pair the watch and Samsung Galaxy phone in Galaxy Wearable.
- Update the watch, Galaxy Wearable and Samsung Health Monitor.
- Open Samsung Health Monitor on the phone, choose ECG and complete setup.
- Sit quietly for approximately 5–10 minutes before recording.
- Clean and dry the sensor; wear the watch snugly above the wrist bone.
- Rest your forearms on a table. On the watch, open Samsung Health Monitor and select ECG.
- Lightly touch the upper button or electrode with a finger from the opposite hand for about 30 seconds without pressing hard or moving.
- Review the result on the watch and synchronized phone. You can use the generated PDF when speaking with a clinician; it is not a self-issued diagnosis.
Samsung’s instructions are available at ECG support and Samsung Health Monitor.
How to enable IHRN
- Record an ECG that is not classified as a poor recording.
- Open Samsung Health Monitor on your phone.
- Tap Get started on the ECG home screen.
- Follow the prompts to enable irregular heart rhythm notifications.
Labels and menu wording can vary by model, software version and country.
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“Atrial fibrillation”
The algorithm classified that short recording as consistent with AFib. It is not physician confirmation. Save it and contact a healthcare professional, particularly if repeated recordings show the same result.
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“Sinus rhythm”
The recording looked regular during that brief interval. It does not prove that intermittent AFib never occurs.
“Inconclusive”
Samsung lists a supported heart-rate range of 50–150 beats per minute on its U.S. page. A rate outside that range, or an irregular rhythm the algorithm cannot classify as AFib, can produce this result.
“Poor recording”
Movement, loose contact, a wet or dirty sensor and signal interference are common causes. Retry while still, with clean, dry skin and a snug fit. Repeated poor recordings should be troubleshot rather than interpreted.
No IHRN notification
No alert is not a clean bill of health. IHRN is intermittent, and Samsung specifically says it is not intended to notify about every episode.
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Failure modes that affect reliability
- Short AFib episodes can fall below IHRN’s studied one-hour notification condition.
- Motion, sweat, lotion, cold or dry skin, hair, loose fit and a dirty sensor can degrade contact.
- Samsung identifies dark tattoos as a possible interference factor.
- The app may not classify arrhythmias other than AFib; Samsung cautions people with known non-AFib arrhythmias to follow medical guidance.
- Regional restrictions and phone compatibility apply. In the U.S., ECG and IHRN require a compatible Samsung Galaxy phone, not an iPhone or arbitrary Android phone.
- Do not use the ECG app with an implanted pacemaker, defibrillator or similar device unless your medical team and applicable instructions say it is appropriate.
See Samsung’s U.S. Instructions for Use and troubleshooting guidance.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What to do after an alert
- As soon as reasonably possible, sit still and record an on-demand ECG.
- Save or share the PDF and note symptoms and timing.
- Contact a healthcare professional for interpretation, especially after repeated AFib classifications.
- Do not start, stop or change medication based only on the watch.
- For chest pain, fainting, severe shortness of breath or stroke signs, contact local emergency services immediately.
An alert without severe symptoms generally calls for prompt clinical follow-up, not automatically an ambulance. Samsung directs users with a possible emergency to emergency services.
Compatibility and regional limits
For U.S. use, Samsung says Samsung Health Monitor requires a compatible Galaxy Watch, compatible Samsung Galaxy phone, installation through the Galaxy Store after pairing, supported software and a supported country or region. The U.S. age requirement is 22 or older. Current U.S. materials identify Galaxy Watch4 and later Wear OS models as the principal current family; older Active2 and Watch3 support depends on software and specific conditions. Check the current phone and device compatibility page and ECG requirements before buying. Availability outside the U.S. can differ.
Buying advice
Galaxy Watch8, Watch8 Classic, Watch Ultra or Watch7
These make sense when you already use a compatible Samsung phone and want ECG, IHRN and Samsung Health alongside ordinary smartwatch functions. Ultra is aimed at rugged outdoor use and larger-battery needs; its form factor does not establish better AFib accuracy. Watch8 Classic suits buyers who prefer a traditional design. Watch7 may be sensible if current stock includes the required software and regional support. Verify the exact model and country before purchasing.
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Apple Watch, Withings or a dedicated ECG
Apple Watch is the practical ecosystem alternative for iPhone owners, not a simple add-on for Samsung-phone users. Withings ScanWatch may suit people prioritizing a health-focused design and longer battery, subject to regional approval and model availability. A dedicated handheld ECG can be preferable when a clinician wants frequent episodic rhythm documentation. Compare the exact device’s regulatory status, export workflow, compatibility and any subscription; pooled brand percentages do not prove one product is best for an individual.
Samsung Health Monitor is presented in the cited materials as included software rather than a separately priced monthly subscription, but terms and hardware prices change. The required Samsung phone can be the largest additional cost. Official information: Samsung Health Monitor.
The practical verdict
A Samsung watch is most useful as a screening and documentation tool. Its ECG can perform strongly when the recording is interpretable and controlled; IHRN provides convenient but intermittent pulse screening with a meaningful false-negative limitation. Treat an alert as a reason to obtain medical confirmation, and treat a normal or absent result as limited evidence rather than reassurance that AFib is impossible.
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