As daily temperatures across the U.S. climb above 90 degrees Fahrenheit, the rate of out-of-hospital cardiac arrest (OHCA) admissions to hospital intensive care units (ICUs) rises in tandem, according to new preliminary research presented at the American Heart Association's Resuscitation Science Symposium 2026. The study, which analyzed data from over 11,000 patients across 10 health systems, found that OHCA admissions were 45% higher on days reaching 91 degrees F and 102% higher at 98 degrees F compared to days at 85 degrees F.
The research, part of the Common Longitudinal ICU Format Consortium (CLIF), also revealed stark disparities: people ages 65 and older had a 48% higher admission rate for OHCA at 90 degrees F versus 67 degrees F, and women were admitted at a rate 33% higher on extreme heat days. These findings underscore the growing burden of climate-related health emergencies on vulnerable populations and the hospitals that serve them.
Cardiac arrest occurs when the heart's electrical system abruptly malfunctions, stopping blood flow to the brain and vital organs; approximately 90% of people who experience OHCA do not survive, according to the American Heart Association. While extreme heat has long been linked to increased cardiac risk, this study is among the first to quantify its impact on ICU admissions specifically. "Heatwaves are becoming more frequent and intense nationally, causing additional strain on communities and emergency services, as well as on hospitals who must absorb the influx of climate-related illnesses," said Peter Graffy, Ph.D., M.P.H., a postdoctoral fellow at the University of Chicago and lead author. "ICU beds, equipment and staff are limited, and sudden increases in critically ill patients can quickly overwhelm hospital resources if we are not ready."
Despite the surge in admissions, the study found that overall outcomes—including survival rates, discharge status, and length of stay—were similar for patients admitted during heat waves compared to cooler days. However, those admitted on days 90 degrees F or above required more interventions for low blood pressure and continuous dialysis for kidney dysfunction, indicating greater clinical complexity. "We were surprised to find that outcomes were not that different," Graffy said. "We think this is likely a testament to clinicians and care teams both in the emergency department and ICU to effectively stabilize these individuals."
The implications for health systems are significant. As extreme heat events become more common, hospitals must prepare for surges in critical care demand. Graffy suggests that hospitals could eventually use temperature forecasts to allocate ICU beds, staff, and resources more effectively. "The health effects of extreme heat do not stop when an ambulance reaches the hospital," he said. "Our findings show that heat is associated with more cardiac arrest admissions and greater needs for advanced critical care interventions, which can strain already limited ICU capacity."
For the public, the message is clear: heat warnings should be taken seriously, especially for older adults and those with medical vulnerabilities. "At a minimum, everyone should learn the lifesaving skills of CPR and seek medical care as quickly as possible," said Ashish Panchal, M.D., Ph.D., FAHA, chair of the American Heart Association's Emergency Cardiovascular Care Committee. With about 70% of out-of-hospital cardiac arrests occurring at home, preparedness and rapid response are critical.
The research is considered preliminary until published in a peer-reviewed journal. The study was featured in a release link from the American Heart Association, which also provides resources on Cardiac Arrest vs. Heart Attack and its Nation of Lifesavers initiative. For more details, the Link to abstract and the Resuscitation Science Symposium 2026 Online Program Planner are available. Additional information can be found in the AHA news release Extreme heat is rising – and so is the risk to your heart and the scientific statement Nonoptimal Temperature and Cardiovascular Health.
