When heat waves settle in, cardiovascular events climb sharply, and adults past 65 shoulder most of the added risk.
A study published in Circulation in October 2023 tied extreme heat days between 2008 and 2019 to roughly 1,651 excess cardiovascular deaths a year in the United States.
The same University of Pennsylvania team, led by Sameed Ahmed M. Khatana, projected that in a warming climate the increase in heat-linked cardiovascular deaths would be 2.9 to 3.5 times greater in people 65 and older than in adults aged 20 to 64.
Four mechanisms drive that vulnerability. To shed heat, the heart pumps faster and pushes more blood to the skin.
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Fluid losses concentrate the blood and can raise clotting risk. Losses of sodium and other electrolytes can nudge the heart into abnormal rhythms. And when nights stay hot, the cardiovascular system loses the cool-down window it usually gets after dark.
"Heat forces the heart to work harder. When your body is trying to cool down, your heart rate increases and your blood vessels expand," said Manesh R. Patel, volunteer president of the American Heart Association, in a July 2026 AHA news release.
Why older hearts feel it more
Aging blunts the body's cooling response. According to a 2025 scientific statement from the European Society of Cardiology, published in the European Heart Journal, people over 60 show reduced sweating, weaker blood-vessel dilation, and a smaller rise in cardiac output when heat hits, all of which limit how efficiently the body dumps excess warmth.
The temperature math is unforgiving. A meta-analysis of 266 studies, summarized in the European Heart Journal, found that each 1°C rise above regional heat thresholds is associated with a 2.1 percent increase in overall cardiovascular mortality, with stroke risk climbing 3.8 percent and acute coronary syndrome 3.5 percent per degree.
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More than 60,000 heat-related deaths were recorded across Europe in the summer of 2022, even after heat-warning systems had been rolled out across much of the continent.
What actually helps
Public-health guidance is boring on purpose because it works. The American Heart Association advises drinking water before, during, and after time outdoors, staying out of the sun during the hottest part of the day (roughly noon to 3 p.m.), and taking regular breaks in the shade or a cool room. Lightweight, light-colored clothing helps the body offload heat.
Two medication groups deserve extra caution. Diuretics, often prescribed for heart failure and high blood pressure, promote fluid and sodium loss that heat exposure can amplify, raising the risk of electrolyte imbalance and arrhythmia.
Beta-blockers are also on the AHA's list of heart drugs that can exaggerate the body's response to heat, along with ACE inhibitors and calcium channel blockers.
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The association is explicit that patients should not stop their medication on their own. Anyone on these drugs who is planning summer activity should talk to their doctor about how to manage hydration and exposure.
Warning signs of heat exhaustion include headache, dizziness, cool and clammy skin, nausea, and a fast, weak pulse. Heat stroke, defined by a core body temperature at or above 103°F, is a medical emergency and calls for 911.
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