Heatwaves Increase Risk Of Cardiac Arrest, Study Finds

TUESDAY, Nov. 3, 2026 (HealthDay News) — More hearts are stopping as summer temperatures break 90 degrees, a new study says.

Hospital admissions for cardiac arrest are 45% higher at 91 degrees and more than double that at 98 degrees outdoors, compared to days with 85-degree heat, researchers are slated to report Saturday at an American Heart Association (AHA) meeting in Chicago.

U.S. hospitals need to brace for more cardiac arrests during a heatwave, researchers warned.

“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 researcher Peter Graffy, a postdoctoral fellow in pulmonary and critical care at the University of Chicago.

“This is important because ICU beds, equipment and staff are limited, and sudden increases in critically ill patients can quickly overwhelm hospital resources if we are not ready,” he said in a news release.

Cardiac arrest occurs when the heart stops pumping due to a malfunction in its electrical system, researchers said in background notes.

About 90% of people who experience a cardiac arrest outside a hospital do not survive, and those lucky few who do may face a long recovery, researchers said.

“People who are resuscitated after out-of-hospital cardiac arrest are usually admitted to an intensive care unit because they are often unconscious and unable to breathe independently,” Graffy said. “They may require advanced life support for several days or weeks while patients’ families wait to see if their loved one regains consciousness.”

Extreme heat has been known to increase risk of cardiac arrest, and climate change could mean more days of heightened risk for these life-threatening heart emergencies, researchers said.

For the new study, researchers analyzed data from 10 U.S. health systems between 2018 and 2024. During that period, more than 11,000 people with cardiac arrest were admitted to an ICU.

About half of the patients were admitted during warm seasons, and 270 during extreme heat of 90 degrees or more.

Results showed that cardiac arrest admissions to the ICU steadily increased with temperatures greater than 90 degrees. Compared to 85-degree heat, results showed:

• A 45% increased risk at 91 degrees or higher

• A 65% increased risk at 93 degrees

• A 102% increased risk at 98 degrees

Seniors 65 and older had the worst risk, researchers found. They had a 48% higher admission rate for cardiac arrest at 90 degrees compared to 67 degrees.

Women also were more likely to suffer cardiac arrest, with a rate 33% higher on days with extreme heat.

People admitted for cardiac arrest on hot days were more likely to need additional treatment for low blood pressure and kidney damage, researchers found.

However, survival rates and health upon discharge were about the same for all people who had a cardiac arrest, regardless of whether they succumbed on a hot or a balmy day.

“We were surprised to find that outcomes were not that different between the two groups,” Graffy said. “We had assumed that since extreme heat typically contributes to multi-organ system dysfunction that the rates of death would be higher among the people whose (cardiac arrest) was potentially influenced by heat." 

But, he said, this was not the case.

"We think this is likely a testament to clinicians and care teams both in the emergency department and ICU to effectively stabilize these individuals with (cardiac arrest) upon admission to give them the best chance at recovery,” Graffy added.

Even though hospitals are taking good care of these patients, a surge in cardiac arrest cases during a heat wave can put a severe strain on ICUs, he noted.

“The health effects of extreme heat do not stop when an ambulance reaches the hospital. 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,” Graffy said.

As extreme heat becomes more common, he said, healthcare systems must adapt and prepare.

“Our goal is that hospitals could one day use temperature forecasts in a data-driven way to adequately prepare ICU beds, staff, resources and coordination between emergency departments and intensive care units,” Graffy said.

AHA spokesman Dr. Ashish Panchal agreed that “heat warnings should be taken seriously because extreme heat can have consequences that extend from the home all the way through to the ICU.” He reviewed the findings.

“We also know that about 70% of cardiac arrests that happen outside of a hospital happen at home, and people need to be prepared: at a minimum, everyone should learn the lifesaving skills of CPR and seek medical care as quickly as possible,” said Panchal, a professor of emergency medicine at Ohio State University.

The AHA meeting takes place Friday through Monday in Chicago. This study is part of a resuscitation science symposium scheduled to occur during the meeting.

Findings presented at medical meetings should be considered preliminary until published in a peer-reviewed journal.

More information

The U.S. Centers for Disease Control and Prevention has more on heat and health.

SOURCES: American Heart Association, news release and abstract, Nov. 2, 2026