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Extreme heat causes strain as the body cools itself down through sweating and the heart pumps more blood to the skin's surface. 

"You then become vulnerable to dehydration, and then your blood pressure drops, your heart rate goes up and that's enough to trigger either a heart attack or an episode of heart failure in patients who have a history of heart disease," said Saeed, who is also a spokesperson for the Heart and Stroke Foundation. 

People who have had strokes can have symptoms such as seizures or fainting, she said, noting that studies show hospitalizations for both heart disease and stroke increase in extreme heat.  

Staying hydrated is a critical way for people to protect themselves, so Saeed tells her patients to continuously drink water throughout the day and not to just drink a large quantity once. 

The foundation recommends staying out of the sun during the peak hours of 11 a.m. and 3 p.m. and to consider visiting libraries, malls or community cooling spaces if people don't have air conditioning at home. 

"Even a few hours a day of being in an air-conditioned surrounding can cool your body down significantly," Saeed said. 

Taking a lukewarm shower can also help people to cool down, she said, but it's important not to make the shower cold because that can constrict the blood vessels. 

People taking some heart and high blood pressure medications — including diuretics, ACE inhibitors and calcium channel blockers — need to be extra vigilant about staying hydrated.

That's because some medications can make it harder for people to cool down or to lose more fluid, Saeed said.  

"During times of extreme heat, if they become too dehydrated, it can predispose them to heat exhaustion, heat stroke, heart failure, fainting, kidney problems," she said. 

"So it can cause a large amount of problems if they don't stay hydrated enough and stay cool enough."

But Saeed emphasized that it's important for people to keep taking their medications and not to make any changes without consulting their primary-care provider.

Signs of dehydration can include thirst, dark yellow urine, tiredness, dizziness or confusion. 

"If you do find that you're feeling unwell, you're having chest pain, you're short of breath (or) you've fainted, go straight to an emergency room," she said. 

In addition to people with cardiovascular disease, older adults and those who work outside are particularly vulnerable to heat-related illness, Saeed said. 

"The heat can be dangerous for everyone," she said. 

One of the most dangerous heat effects for people in general, not just those with cardiovascular disease, is heat stroke — a medical emergency when the body can no longer regulate its temperature. 

Symptoms of heat stroke can include hot, dry skin that isn't sweaty, confusion or agitation, dizziness or fainting, a fast heart rate, vomiting or diarrhea and headache, the Heart and Stroke Foundation website says.  

If you suspect someone is suffering from heat stroke, call 911 and move them to a cool area.  Drenching the skin with cool water, fanning and ice packs can be useful while waiting for help to arrive. 

The Heart and Stroke Foundation says that despite its name, heat stroke is not the same thing as having a stroke, which is when blood stops flowing to part of the brain. 

This report by ºÃÉ«tvwas first published July 14, 2026.

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