Extreme Temperatures May Raise the Risk of Hospitalization for Heart Failure

Exposure to both unusually cold and unusually hot temperatures may increase the short-term risk of hospitalization for heart failure, according to a new study presented at ESC Congress 2026 and published simultaneously in JACC.

Researchers analyzed nearly 482,000 hospitalizations for heart failure recorded in the Swedish National Patient Register between 2006 and 2021. They examined the relationship between hospital admissions and periods of unusually low or high temperatures.

Cold spells were defined as at least two consecutive days when temperatures fell at or below the 5th percentile of the temperature distribution for the area during October through March. Heat waves were defined as temperatures at or above the 95th percentile during April through September.

The study found that cold spells were associated with an increased risk of heart failure hospitalization within two to six days after exposure. The strongest statistically significant association was observed three to five days later.

Lower ambient temperatures were similarly linked to a higher risk of hospitalization three to six days after exposure, with the clearest increase occurring three to five days afterward.

By contrast, higher temperatures were associated with an increased risk of heart failure hospitalization within zero to three days, suggesting that the effects of heat may occur more rapidly.

Interestingly, the researchers found no statistically significant association between exposure to defined heat waves and heart failure hospitalization.

According to the study authors, the delayed effect of cold exposure and the more immediate risk associated with higher temperatures highlight the need for time-sensitive approaches to patient care. This could include closer monitoring following cold-weather alerts and faster responses during periods of extreme heat.

“To the best of our knowledge, no previous study has examined the short-term associations between extreme temperature events, including cold spells and heat waves, or continuous exposure to non-optimal temperatures and heart failure hospitalizations in a Nordic population,” said Wenli Ni, PhD, the study’s lead author.

The researchers noted that this is an important knowledge gap because countries at high latitudes such as Sweden experience frequent exposure to cold while also becoming increasingly vulnerable to heat as the global climate warms.

In an accompanying editorial, Tiantian Li, PhD, deputy director of the National Institute of Environmental Health at the Chinese Center for Disease Control and Prevention in Beijing, warned against continuing to practice cardiovascular medicine without considering environmental conditions.

“The evidence linking non-optimal temperature to cardiovascular harm is now substantial,” Li said, emphasizing the need to turn the growing body of research into practical early-warning systems rather than simply accumulating more epidemiological data.

The findings were discussed as part of a special ESC–JACC Joint Session at ESC Congress 2026 devoted to environmental threats to cardiovascular health. Experts examined the effects of air pollution, wildfire smoke, temperature extremes and specific components of fine particulate matter, as well as the combined impact of multiple environmental stressors.

The researchers say that understanding these environmental risks could help improve cardiovascular disease prevention and enable clinicians to respond more quickly when vulnerable patients are exposed to dangerous weather conditions.