AI read Apple and Samsung smartwatch heart tracings to flag a weak heart, but the two watches disagreed for 9% of patients

Artificial intelligence that reads the heart tracings recorded by consumer smartwatches may help find people whose hearts are pumping weakly before they feel sick, but the results varied from watch to watch and from day to day, according to a preliminary study presented Nov. 9 at the American Heart Association’s Scientific Sessions in Chicago.

The condition the study looked for, left ventricular systolic dysfunction, happens when the heart’s main pumping chamber squeezes too weakly.  The study defined it as an ejection fraction of 40% or less, meaning the chamber pushes out no more than 40% of its blood with each beat.  It can cause no symptoms at first and, without treatment, can lead to heart failure, the heart association says.  It is usually diagnosed with an echocardiogram, an ultrasound scan of the heart.

How it works

An electrocardiogram, or ECG, records the heart’s electrical signals.  A hospital ECG uses 12 sensors on the chest and limbs.  Apple Watch and Samsung Galaxy Watch models can record a simpler 30-second, single-lead version.  In this study, a separate AI model built by Medical AI Co., a South Korean company, looked at those tracings for subtle signs of a weak pump.

What the study found

Researchers at Incheon Sejong Hospital in South Korea recorded ECGs on both an Apple Watch and a Galaxy Watch, back to back, for 2,211 adults scheduled for an echocardiogram.  The AI sorted people with and without a weak pump about equally well on both watches.  But using the same cutoff, 200 people, or 9%, tested positive on one watch and negative on the other.

Was one watch better?

No, according to what the heart association released. The AI separated people with and without a weak pump “about equally well” on the Apple Watch and the Galaxy Watch, and the release gives no figures showing either brand was more accurate. The disagreements came from the cutoff score the AI used to call a result positive. That cutoff was set in advance using Galaxy Watch tracings, and when the same number was applied to both watches, 200 people landed on opposite sides of it. The release does not say which watch produced more of the positive results. The at-home group can’t settle the question either, because 94% of those patients used a Galaxy Watch.

A second group of 146 patients recorded tracings at home on their own watches, most of them Galaxy Watches.  Among 108 who recorded on at least five days, counting someone as positive only after two positive days out of three cut false alarms in half, from 18 to 9 among 70 people without the condition.  But it caught 31 of 38 people who had it, two fewer than counting a single positive day.  Of people whose results were consistently positive, 81% had the condition confirmed by ultrasound, compared with about 6% of those consistently negative.

“A single smartwatch ECG is a snapshot, and repeated recordings can give different results,” said Dr. Hak Seung Lee, the study author, who is chief medical officer of Medical AI Co. and a cardiologist at Sejong Medical Research Institute.

Limits

The study was done at one hospital among patients already sent for heart scans, many of whom had known heart failure, so the condition was far more common than in the general public.  It did not test whether using the AI leads to earlier treatment or longer lives, and it is a meeting abstract that has not yet been reviewed by outside scientists for a journal.  More research is needed before smartwatch tracings can replace standard heart tests, the heart association says.

Source:  American Heart Association news release, Nov. 9, 2026.