Smartwatches show promise in identifying increased risk of heart failure hospitalization
In a Nature Medicine study led by UHN's Peter Munk Cardiac Centre, researchers evaluated large-scale smartwatch data to assess its ability to signal worsening heart failure risk.
TORONTO, March 20, 2026 /CNW/ - A new study published in Nature Medicine shows that data from a consumer smartwatch can detect early signs of worsening health in people living with heart failure, often days to weeks before unplanned medical care is needed.
Led by researchers at UHN's Peter Munk Cardiac Centre and part of the Transform HF initiative, the study shows that smartwatch data can reliably monitor daily cardiopulmonary fitness in people living with the condition. As the largest study of its kind, it also demonstrates that meaningful, clinically relevant declines in fitness levels can be detected days to weeks earlier than usual.
Notably, a drop of 10 per cent or more in daily cardiopulmonary fitness was associated with a more than three-fold increase in the risk of unplanned health care use, such as hospitalization or urgent treatment, opening the door to more proactive and timely interventions.
"Heart failure often worsens silently between clinic visits. By tapping into information captured through everyday wearable tech, this study shows we can detect significant changes much earlier, and potentially intervene before a health crisis occurs," says Dr. Heather Ross, Head of Cardiology at UHN's Peter Munk Cardiac Centre and co-senior author.
Key findings
The three-month observational study followed 217 people with heart failure as they went about their daily lives. Participants wore an Apple Watch while researchers collected data such as heart rate, physical activity, and oxygen saturation levels. Participants were instructed not to change their usual activity routine.
Using a UHN-developed and externally validated artificial-intelligence model, the research team analyzed patterns in this wearable data to estimate daily cardiopulmonary fitness--a key measure of how well the heart and lungs work together. These smartwatch-based fitness estimates closely matched results from gold-standard clinical exercise testing at the beginning and at the end of the study.
"We couldn't have done this anywhere else. This work reflects UHN's commitment to translating innovation into clinical tools through a highly interdisciplinary team," says Chris McIntosh, Senior Scientist at UHN's Peter Munk Cardiac Centre, and co-senior author of the study.
"By combining clinical insight on day-to-day changes in activity capacity with advanced modelling expertise, we can track activity and physiological signals over time and flag declines that might otherwise be missed between clinic visits."
Impact
Heart failure affects an estimated 64 million people worldwide and is one of the most frequent and costly reasons for hospital admission in Canada, with one in five patients being re-admitted to hospital within a month of being discharged. According to the Canadian Institute for Health Information (CIHI), heart failure consistently ranks among the top five causes of hospitalization nationwide.
The condition is marked by periods of relative stability interrupted by sudden worsening that can lead to emergency visits and hospitalizations. Waiting for infrequent clinic visits can mean that early signs of deterioration may be missed. Despite recent advances, long-term outcomes remain poor, with population studies reporting that nearly half of Canadians living with heart failure die within five years of diagnosis.
Why it matters
The study suggests that monitoring with everyday devices like smartwatches could help identify real-time changes in health without additional tests or added effort from patients, potentially enabling earlier follow-up and more responsive care.
In a separate validation using an independent U.S. cohort of 193 people with heart failure wearing a different consumer wearable platform, similar declines in daily fitness were linked to higher risk of unplanned hospital care and were detected around three weeks before events occurred.
Further research will explore how this wearable monitoring approach could be advanced and integrated into real-world care to improve patient outcomes.
* Apple provided 200 iPhones and Apple Watch devices for the study, provided feedback on the manuscript, and collaborated with all authors to build the study-specific mobile application. The authors declared no other competing interests.
** B-roll and photos available upon request.
About TRANSFORM HF
TRANSFORM Heart Failure is a strategic initiative of the Ted Rogers Centre for Heart Research and the University of Toronto dedicated to digital health innovation and equitable access to high-quality heart failure care. The initiative brings together more than 300 members and over 80 national and international partners to co-design and implement technologies that improve heart failure diagnosis, monitoring, and management in real-world settings. www.transformhf.ca
About University Health Network
UHN is Canada's Hospital -- ranked #2 in the world, #1 in Canada. With 10 sites and more than 44,000 TeamUHN members, UHN consists of Toronto General Hospital, Toronto Western Hospital, Princess Margaret Cancer Centre, Toronto Rehabilitation Institute, The Michener Institute of Education and West Park Healthcare Centre. As Canada's top research hospital, the scope of biomedical research and complexity of cases at UHN have made it a national and international source for discovery, education and patient care. UHN has the largest hospital-based research program in Canada, with major research in neurosciences, cardiology, transplantation, oncology, surgical innovation, infectious diseases, genomic medicine and rehabilitation medicine. UHN is a research hospital affiliated with the University of Toronto. www.uhn.ca
SOURCE University Health Network
Media Contacts: Ana Fernandes, Manager, External Communications, University Health Network, [email protected]; Leslie Whyte Zhou, Senior Communications Advisor, Media Relations, University Health Network, [email protected]
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