Extreme Heat and Cold Are Growing Heart Risks, and Health Systems Are Not Yet Ready

When the temperature climbs past a hundred degrees, a cardiologist or internist may find a question sitting in the exam room that medicine cannot yet answer: should a patient's heart medications change? Dr. Arnab Ghosh, an associate professor of medicine at Weill Cornell and an internist at NewYork-Presbyterian/Weill Cornell Medical Center, put it plainly. Right now, he said, we just don't know.

That admission sits inside a new scientific statement from the American Heart Association, published in Circulation, written by experts at Weill Cornell Medicine and other leading institutions. The statement concludes that extreme heat and extreme cold are growing cardiovascular risks, capable of triggering heart attacks, strokes, heart failure, and sudden cardiac death. Ghosh led the development of its policy section.

Cold has historically been the bigger killer. Cold days are far more frequent than hot ones, so they have accounted for more cardiovascular deaths. But the report warns that extreme heat events are increasing in frequency, intensity, and duration, and that heat-related deaths may eventually outweigh any decline in cold-related mortality. The year 2024 was already the hottest since the National Oceanic and Atmospheric Administration began keeping records in 1880.

The mechanism is physical. In hot weather the body cools itself by widening blood vessels and sweating more. That releases heat, but it also lowers blood pressure and reduces the body's fluid levels. The heart compensates by beating faster and pumping harder, a strain that can be dangerous for people with cardiovascular disease. Some heart medications, diuretics among them, make people lose water, adding to the load and potentially bringing on a heart attack.

The risk is not spread evenly. Older adults face some of the highest, because aging reduces the body's ability to regulate temperature. Pregnant individuals, infants, and outdoor workers are also vulnerable, as are people with low incomes, who often live in areas with little shade and may lack air conditioning.

The authors say solutions have to work at several levels. On the research side, the statement points to unanswered questions: what temperature threshold endangers people at risk of cardiovascular problems, what repeated long-term heat exposure does to the body, and how medications interact with heat stress, especially when a person takes several at once.

The statement also turns to the health care system itself, which accounts for about 8.5% of greenhouse gas emissions in the United States. Everything from the energy to run MRI machines to the anesthetics used in operating rooms contributes. Providers can be more conservative about the procedures they recommend and the disposable equipment they use, though only so far without compromising patient safety. Ghosh suggests the system may need reimagining, with more telehealth visits, for example, cutting travel emissions. He called for a fundamentally different system that delivers the same health benefits while also being good for the planet.

For policymakers, the researchers highlight keeping energy costs affordable so people can run their air conditioning, and providing cooling centers for those who need somewhere to escape the heat. Trees matter too. Ghosh recently published a Nature Communications paper on urban tree planting, finding that the best way to cool cities is not simply planting more trees but building dense, continuous canopies close to homes, streets, and public spaces where residents are most exposed.

Cutting current and future greenhouse gas emissions would be the best way to limit heat's role in heart disease, Ghosh said, but learning to live in a hotter world matters now. Heat is a problem today, he said, and the field needs more tools and creative solutions. The research questions on thresholds, long-term exposure, and medication are where to watch next.