An alert buzzed from an Apple Watch while a man in Maine was sitting quietly. His heart rate had fallen to 32 beats per minute, which typically indicates that there is a serious problem with his chest. He hadn’t experienced much. Perhaps a bit worn out. He received a pacemaker in a matter of days. Apparently, the watch had detected something that his body had not yet made public.
These kinds of stories are getting more difficult to ignore. For many years, the notion that a consumer wearable could forecast cardiac events seemed like science fiction wrapped in marketing jargon, the kind of assertion that is printed on glossy packaging with terms like “wellness” and “lifestyle.” However, there has been a subtle change in cardiology circles, and most people are unaware of how credible this change is.
| Category | Details |
|---|---|
| Companies Covered | Apple Inc. (Apple Watch) & Garmin Ltd. |
| Key Technology | Single-lead ECG sensors, irregular rhythm notifications, optical heart rate monitoring, blood oxygen (SpO2) |
| FDA Clearance | Apple Watch ECG cleared for atrial fibrillation detection; irregular rhythm notifications also FDA-approved |
| Accuracy (Heart Attack Detection Study) | 93–95% accuracy in identifying heart attacks via smartwatch ECG (JAMA Cardiology, 2020) |
| Key Research Institution | University Health Network, Toronto — Peter Munk Cardiac Centre |
| Heart Failure Study Size | 217 participants monitored over 3 months; findings published in Nature Medicine (2026) |
| Critical Limitation | Cannot replace 12-lead ECG; only 1 lead available; requires physician interpretation for diagnosis |
| Hospitalization Risk Signal | 10%+ drop in daily cardiopulmonary fitness = more than 3× increased risk of unplanned hospital admission |
| Complementary Diagnostics | Blood biomarkers (ApoB, LDL, HDL, Lp(a), hs-CRP, troponin) remain essential for full cardiovascular risk assessment |
| Expert Reference | Dr. Peter Libby, Professor — Harvard Medical School / Brigham and Women’s Hospital |
| Emergency Protocol | Chest pain = call 911 immediately. Do not rely on smartwatch as primary diagnostic tool during a cardiac event. |
Data from an Apple Watch could identify early warning signs of worsening heart failure, sometimes days or even weeks before a patient needed emergency care, according to a recent study published in Nature Medicine by researchers at the University Health Network in Toronto. Over the course of three months, the study monitored 217 individuals with heart failure and recorded their heart rate, physical activity, and oxygen saturation while they went about their daily lives, such as walking to the store, sitting at home, or strolling through a mall. A participant’s risk of an unscheduled hospital stay increased by more than three times when their estimated cardiopulmonary fitness fell by ten percent or more. The conclusion is not marginal. That is a significant clinical signal that was recorded by a gadget that most people purchase to monitor their morning runs.
Chris McIntosh, a senior scientist at UHN who co-led the study, stated, “We’re seeing what happens to their heart rate when they’re walking at the mall, on the street, or at home.” That sentence contains something worth pondering. A 15-minute clinic visit or a stress test in a monitored hospital hallway with a clinical team supporting you from behind are examples of how traditional cardiology records snapshots. This is not the same. This is an ongoing, non-intrusive, real-world observation of the actual behavior of a failing heart in daily life.
It’s difficult to ignore how far wearables have come since their inception. Fitbit tracked steps ten years ago. These gadgets are currently using AI models that were developed using cardiac data gathered from thousands of patients. The FDA has approved the Apple Watch’s ECG feature, which captures a single-lead ECG, to identify atrial fibrillation, the most prevalent irregular heartbeat and a major risk factor for stroke. In the Apple Heart Study, atrial fibrillation was later confirmed in 84% of participants who received an irregular rhythm notification. That isn’t a device. That is a tool for screening.
However, the limitations are real and should be acknowledged. Technically, a 12-lead ECG (12 angles of electrical activity through the heart simultaneously) and a blood test for troponin, the protein released when heart muscle is dying, are used to diagnose a heart attack. Only one lead is recorded by the Apple Watch. Certain heart attacks would just not appear on it. Cardiologist Dr. Peter Libby of Harvard-affiliated Brigham and Women’s Hospital was as straightforward as ever: “If you have chest pain or discomfort, don’t mess around with your smart watch — call 911.” That is still the right advice, and it shouldn’t be buried in any responsible account of this technology.
However, Dr. Libby added, “Coupling wearable devices with artificial intelligence will transform our ability to monitor and predict heart disease.” He stated it as a measured evaluation of the trajectory’s direction rather than with promotional zeal. Atrial fibrillation, heart failure, and possibly even early cardiac injury years before symptoms manifest could eventually be detected by the algorithms being developed today, which have been trained on large ECG datasets and calibrated against real-world outcomes. Although the precise date of that becoming a clinical reality is still unknown, the rate of research indicates that it may not be as distant as previously thought.
For its part, Garmin has been discreetly developing its own cardiac health features, such as HRV (heart rate variability) monitoring and resting heart rate trends, which some researchers think could be early markers of physiological stress. Although the company has less aggressively positioned itself in the clinical space than Apple, its devices are worn by both serious athletes and older adults, who in one way or another have a reason to be concerned about the health of their hearts in between checkups.
We seem to be at a truly uncertain turning point. The clinical frameworks intended to validate the technology are being surpassed by the technology itself. It makes sense that doctors are concerned about receiving an overwhelming number of ECG alerts from nervous patients whose watches indicated something unclear at two in the morning. Agencies in charge of regulations are acting cautiously. However, data continues to come in, study after study, demonstrating that these tiny devices are detecting actual signals in actual people before those people wind up in emergency rooms.
In the words of Paula Vanderpluym, a heart failure patient from Toronto who took part in the UHN study. She said, “The whole idea that doctors could use this data to predict if you’re going to get worse, and intervene before you need to be admitted into a hospital,” was sufficient justification for taking part. She also brought up a point that is often overlooked in clinical discussions: people who live far from major cardiac centers in rural areas might eventually have continuous access to the kind of monitoring that currently necessitates a hospital visit. That is not a minor issue.
It’s possible that your wristwatch already knows more about your heart than you realize. It’s also possible that it will take a few cautious years for it to reach its true moment, when it becomes a legitimate first line of cardiac screening. It’s getting harder and harder to deny that this is just a fitness tracker. Here, something is taking place. The cardiologists are observing.
