As daily temperatures climb above 90 degrees Fahrenheit across the United States, hospitals are seeing a corresponding rise in intensive care unit admissions for out-of-hospital cardiac arrest (OHCA), according to new preliminary research presented at the American Heart Association’s Resuscitation Science Symposium 2026. The findings underscore a looming public health challenge: as extreme heat events become more frequent and intense, hospitals must prepare for a surge in critically ill patients that could overwhelm limited ICU resources.
The study, which analyzed data from more than 11,000 OHCA patients across 10 health systems between 2018 and 2024, found that the rate of OHCA admissions to the ICU increased steadily as temperatures rose. Compared with days reaching 85 degrees Fahrenheit, OHCA admissions were 45% higher at 91 degrees Fahrenheit and 102% higher at 98 degrees Fahrenheit. Women were admitted at a rate 33% higher on extreme heat days, and adults aged 65 and older saw a 48% higher admission rate at 90 degrees Fahrenheit compared with 67 degrees Fahrenheit.
“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 of the study. “ICU beds, equipment and staff are limited, and sudden increases in critically ill patients can quickly overwhelm hospital resources if we are not ready.”
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. Those who are resuscitated often require advanced life support in the ICU for days or weeks.
While the study found that heat exposure was associated with more ICU admissions and greater need for interventions such as treatment for low blood pressure and continuous dialysis for kidney dysfunction, it also revealed a surprising finding: overall survival and discharge outcomes were similar to those admitted during cooler periods. “We were surprised to find that outcomes were not that different between the two groups,” 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.”
However, the increase in ICU admissions during heat waves has profound implications for health systems. “The health effects of extreme heat do not stop when an ambulance reaches the hospital,” Graffy 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.” He added that hospitals could one day use temperature forecasts to adequately prepare ICU beds, staff and resources.
The research adds to a growing body of evidence on the cardiovascular dangers of extreme heat. The American Heart Association has previously highlighted the issue in its scientific statement on Nonoptimal Temperature and Cardiovascular Health and in a news release warning that extreme heat is rising – and so is the risk to your heart.
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. The Association encourages the public to join its Nation of Lifesavers initiative and to understand the difference between Cardiac Arrest vs. Heart Attack.
The study’s abstract is available via the Link to abstract, and further details about the conference can be found on the About Resuscitation Science Symposium 2026 page. The findings are considered preliminary until published in a peer-reviewed journal.
