Study Confirms Apple Watch Can Detect Abnormal Heart Rhythm With 97% Accuracy

The heart rate monitors built into the Apple Watch and other wearable devices can detect abnormal heart rhythms with 97 percent accuracy, according to a new study conducted by the team behind the Cardiogram app for Apple Watch in conjunction with researchers at the University of California, San Francisco.

More than 139 million heart rate and step count measurements were collected from 9,750 users of the Cardiogram app who also enrolled in the UC San Francisco Health eHeart Study, with the data used to train DeepHeart, Cardiogram's deep neural network.

cardiogram
Once trained, DeepHeart was able to read heart rate data collected by wearables, distinguishing between normal heart rhythm and atrial fibrillation with a 97 percent accuracy rate, both when testing UCSF patients with known heart issues and Cardiogram participants.

At a 97 percent accuracy rate, Cardiogram's study suggests the Apple Watch alone does a better job of detecting abnormal heart rhythms than FDA-approved accessory KardiaBand. From Cardiogram co-founder Johnson Hsieh:

97% accuracy refers to the c-statistic, or area under the sensitivity-specificity curve. Surprisingly, both the sensitivity and specificity of DeepHeart were even higher than an FDA-cleared Apple Watch ECG attachment -- 98% (vs 93%) sensitivity and 90% (vs 84%) specificity.

Published in JAMA Cardiology this morning, the study confirms the results from a similar preliminary study done in May of 2017. According to Cardiogram, today's study marks the first peer-reviewed study in a medical journal that demonstrates popular wearables from companies like Apple, Garmin, Polar, LG, and others can detect a major health condition.

Atrial fibrillation, or an abnormal heart rhythm, is a condition that can be indicative of major health problems and it can lead to heart failure and stroke. Atrial fibrillation often goes undiagnosed, which is where the Apple Watch and other wearables can help. The Apple Watch won't replace a traditional EKG, but it can alert people to a problem much earlier than it might otherwise be detected. From the study's conclusion:

This proof-of-concept study found that smartwatch photoplethysmography coupled with a deep neural network can passively detect AF but with some loss of sensitivity and specificity against a criterion-standard ECG. Further studies will help identify the optimal role for smartwatch-guided rhythm assessment.

In addition to studies on the Apple Watch's ability to detect atrial fibrillation, Cardiogram and UCSF have also been working to determine if the Apple Watch heart rate monitor can also detect conditions like hypertension, sleep apnea, and early signs of diabetes. Preliminary studies have suggested all of these conditions could be spotted in data collected by Apple Watch and other common wearable devices.

Apple has been working with researchers at Stanford on its own study to determine whether the heart rate sensor in the Apple Watch can be used to detect abnormal heart rhythms and common heart conditions. While in the study, if an abnormal heart rhythm is detected, participants will be contacted by researchers and asked to wear an ePath monitor to test heart health.

Apple Watch owners can sign up to participate in the Apple Heart Study by downloading and installing the Apple Heart Study app. Those who want to join Cardiogram's studies can install the Cardiogram app and sign up to join the mRhythm study.

Related Roundup: Apple Watch 10
Buyer's Guide: Apple Watch (Neutral)

Popular Stories

iPhone 17 Pro 34ths Perspective

iPhone 17 Pro Launching Later This Year With These 10 New Features

Sunday March 23, 2025 10:00 am PDT by
While the iPhone 17 Pro and iPhone 17 Pro Max are not expected to launch until September, there are already plenty of rumors about the devices. Below, we recap key changes rumored for the iPhone 17 Pro models as of March 2025: Aluminum frame: iPhone 17 Pro models are rumored to have an aluminum frame, whereas the iPhone 15 Pro and iPhone 16 Pro models have a titanium frame, and the iPhone ...
macbook pro blue green

When Will Apple Release the M5 MacBook Pro?

Wednesday March 26, 2025 4:53 pm PDT by
Apple regularly refreshes the MacBook Pro models, and a new version that uses M5 series chips is in the works. Apple just finished refreshing most of the Mac lineup with M4 chips, and now it's time for the M5. Rumors suggest that we could see the first M5 MacBook Pro models this fall. Design There have been no rumors of a design update for the M5 MacBook Pro models that are coming this...
iOS 18

iOS 18.4 Expected Next Week - Here Are the Release Notes

Friday March 28, 2025 2:01 pm PDT by
With the second release candidate of iOS 18.4 that Apple seeded out today, the company finally provided us with release notes that give a full rundown on what to expect. There's an Apple Vision Pro app, new Apple Intelligence features for notifications and additional language support, plus an Apple News Food feature for Apple News+ subscribers, and several updates that should improve the...
Facebook Feature

Facebook's New iPhone App Feature Turns the Clock Back to 2007

Thursday March 27, 2025 1:59 pm PDT by
In the mid-to-late 2000s, Facebook was all about staying connected with friends and family. However, as the social media platform added new features and grew over time, that core experience began to get drowned out. That changes starting now, according to Meta, which today introduced a new feature that will "bring back the joy" of classic Facebook. Specifically, Meta has redesigned the...
iOS 18 4 Ambient Music Control Center

How to Use iOS 18.4's New Ambient Music Feature in Control Center

Thursday March 27, 2025 7:45 am PDT by
The upcoming iOS 18.4 update for the iPhone adds an Ambient Music feature to Control Center. Below, we take a closer look at how it works. iOS 18.4 is currently in beta, so the Ambient Music feature is not widely available yet. The update will likely be released to the general public next week. To use the feature on iOS 18.4, open Control Center and tap on the plus sign in the top-left...
Foldable iPhone 2023 Feature 1

'iPhone Fold' to Feature Metallic Glass Hinge That Resists Deformation

Thursday March 27, 2025 4:21 am PDT by
Last week, we covered a report claiming that Apple's book-style foldable iPhone (or "iPhone Fold," as we are provisionally calling it here) will use liquid metal hinges to improve durability and help minimize screen creasing. Today, a Chinese leaker provided more details on the properties of this hinge material that help to clarify why Apple chose it for its first foldable device. According...
Magic Mouse Green

What to Expect From the Magic Mouse 3

Saturday March 29, 2025 10:15 am PDT by
Apple is reportedly working on a new Magic Mouse. Below, we recap what to expect. The two key rumors for the Magic Mouse 3 so far include a relocated charging port, along with a more ergonomic design. It was briefly rumored that the Magic Mouse 3 would also feature voice control, but that was misinterpreted information. Relocated Charging Port While the Magic Mouse switched from...
Foldable iPhone 2023 Feature Homescreen

Six Things to Know About Apple's Upcoming Foldable iPhone

Friday March 28, 2025 3:54 pm PDT by
We've been hearing rumors about a foldable iPhone for almost a decade now, but it looks like we might finally see the device come to fruition in 2026. We're going to be waiting many more months for the foldable iPhone, but so far we're hearing good things. Apple wants to make it creaseless. It's taken Apple multiple years to design a foldable iPhone that it's satisfied with because Apple ...
Apple Lumon Terminal Pro

Apple's Mac Site Features Fictional 'Lumon Terminal Pro'

Wednesday March 26, 2025 12:19 pm PDT by
Apple is going all out with promotions for the popular Severance Apple TV+ show today, and as of right now, you'll find a new "Lumon Terminal Pro" listed on Apple's Mac site. The Lumon Terminal Pro is designed to look similar to the machines that Severance employees like Mark S. and Helly R. use for macrodata refinement. The Terminal features a blue keyboard, a small display with wide...

Top Rated Comments

justperry Avatar
92 months ago
Another paid research. It's the same off-the-shelf HRM as other watches.
Seems like you can't read, there are other brands mentioned/involved in the article, like LG and Polar amongst others.

(Macrumors) today's study marks the first peer-reviewed study in a medical journal that demonstrates popular wearables from companies like Apple, Garmin, Polar, LG, and others can detect a major health condition.
Why so negative, I think this is a good thing.
Score: 21 Votes (Like | Disagree)
370zulu Avatar
92 months ago
My AW3 is a requirement by my wife after my heart attack a while back. I wear it while I sleep and have it set to alert me if my HR goes above 120. When I was ill and had a fever, my HR went up and over 120 a few times and I had the watch wake me while I was trying to rest. This does make wife and I feel better about having some kind of warning that I may need to seek medical attention.

For that, the price of AW3 is definitely worth it for me despite the naysayers.
Score: 11 Votes (Like | Disagree)
Cesar Battistini Avatar
92 months ago
Personally I don't find the Apple Watch heart rate sensor to be that accurate. When working out, it will regularly be off by a factor. To me, this means it's missing every other heartbeat. For example, my resting is ~70; when doing a cardio workout it will go up to 150 or so, then suddenly down to 75. Definitely not right, I am in the middle of cardio and feeling it, it's not 75.
Is the watch tight enough? That usually solves the problem.
Score: 8 Votes (Like | Disagree)
oneMadRssn Avatar
92 months ago
I went out drinking with co-works one evening after work and my watch alerted me that my heart rate was over 120/125 or whatever it was. Was it because I was drinking or was it an error?
Personally I don't find the Apple Watch heart rate sensor to be that accurate. When working out, it will regularly be off by a factor. To me, this means it's missing every other heartbeat. For example, my resting is ~70; when doing a cardio workout it will go up to 150 or so, then suddenly down to 75. Definitely not right, I am in the middle of cardio and feeling it, it's not 75.
Score: 7 Votes (Like | Disagree)
NinjaHERO Avatar
92 months ago
Very cool. I look forward to the day my tech can tell the doctors what I've broken. :-)
Score: 7 Votes (Like | Disagree)
citysnaps Avatar
92 months ago
My AW3 is a requirement by my wife after my heart attack a while back. I wear it while I sleep and have it set to alert me if my HR goes above 120. When I was ill and had a fever, my HR went up and over 120 a few times and I had the watch wake me while I was trying to rest. This does make wife and I feel better about having some kind of warning that I may need to seek medical attention.

For that, the price of AW3 is definitely worth it for me despite the naysayers.
That's a great story. Thanks for sharing!
Score: 5 Votes (Like | Disagree)