How the Heat Can Affect Your Heart

You’ve just checked the forecast, and it looks like a heat wave is on its way. Whether you’re excited about those scorching days or dreading them, your heart doesn’t have much of a say in the matter. It’s got to keep pumping blood through your body, no matter the temp.

Maybe you’ve noticed your pulse pick up the pace when you’re sitting in the sun. Or perhaps you’ve felt a little woozy after a long afternoon of gardening. So, now maybe you’re wondering: Does the heat make a difference when it comes to your heart? And if so, should you do anything about it?

Exercise physiologist Michael Crawford, ACSM-CEP, who specializes in cardiac rehabilitation, explains.

Why heat impacts your heart

Heat makes your heart work way harder than usual.

When it’s hot, your body radiates warmth to cool you down. That might feel counterintuitive. But shedding some heat from inside your body helps your core body temperature decrease.

How this happens is awesome and complex. Your autonomic nervous system sends signals that tell your heart to beat faster and your blood vessels to expand. This means your heart quickly pumps out blood, and your blood vessels open up more to accommodate the flow.

“These important changes allow more blood to flow through arteries and veins close to your skin’s surface,” Crawford explains. “When blood travels there, it’s able to lose a bit of warmth to the air around you.”

That’s a good thing when it comes to avoiding heat-related illnesses, like heat exhaustion or heat stroke. As blood loses some warmth, it helps regulate your body temperature.

But these changes also force your heart to pull some serious overtime.

“Your cardiovascular system really ramps up efforts to radiate heat and cool you down,” he continues. “This makes your heart rate go up and your sweat increase — and that can potentially lead to your blood pressure going down. The longer you’re in the heat, the greater the toll on your heart.”

Crawford breaks down these effects on your heart rate and blood pressure.

High temps lead to a higher heart rate

For every degree your body’s internal temperature rises in the heat, your heart rate increases by about 10 beats per minute (bpm). That’s a lot, even if you’re just basking on a lounge chair.

“It’s possible for the heat to get your resting heart rate above 100 beats per minute (bpm), which means you’re experiencing tachycardia,” Crawford says.

Now, imagine you’re out for a jog or mowing the lawn. No matter the weather, your heart must pump harder to meet those physical demands. Add heat into the mix, and your heart rate could quickly soar higher than usual.

Heat can cause your blood pressure to drop

When your blood vessels expand to let more blood flow through, your blood pressure goes down. A slight drop won’t affect you much. But the hotter you get, the faster your heart pumps out blood — and the more those vessels have to widen.

“This can make your blood pressure fall below 90/60 mm Hg — a state we call hypotension,” Crawford explains. “That’s lower than normal and can lead to problems if not corrected quickly.”

Warning signs that your heart may be in trouble

Usually, a brief spike in your heart rate or drop in your blood pressure isn’t a cause for concern. Your body’s simply doing its job to help cool you down. You may not even feel any different.

But if your heart rate gets too high or your blood pressure gets too low, you might start to feel the effects. It’s also possible to develop dehydration, heat exhaustion or heat stroke. Because all these issues share lots of symptoms in common, you might not be able to tease out what’s happening in the moment.

In general, some red flags to watch out for include:

• Dizziness or fainting
• Feeling very tired or weak
• Headache
• Heart palpitations
• Muscle cramps
• Nausea or vomiting
• Shortness of breath

If you feel any of these symptoms, it’s time to take a break from the heat. You should also alert a healthcare provider. They may ask you to come in for a check-up to make sure you’re OK.

And seek medical care immediately if you have signs of heat stroke. These include blurred vision, confusion, dizziness, fainting and slurred speech.

Risk factors

Certain medical conditions and medications can decrease your ability to tolerate heat. In other words, you’re more sensitive to heat — and you may start to feel the effects sooner than others.

Take extra care in the heat if you have any of these conditions:

• Cardiovascular disease
• Dysautonomia
• Kidney disease
• Multiple sclerosis
• Orthostatic hypotension
• Overweight/obesity
• Respiratory conditions, like asthma or COPD

You may also have reduced heat tolerance if you take:

• Blood pressure meds (antihypertensives)
• Diuretics, which lower blood volume

Staying heart-healthy in the heat

Heat affects all of us a little differently. It’s a good idea to talk to a healthcare provider to learn if you should take it easy when the temps are high. These conversations are especially important if you’re over age 65 or have any of the risk factors listed.

Whether you’re in the heat for work or for play, try to:

• Take breaks in the shade or in air conditioning.
• Drink plenty of water to stay hydrated.
• Wear light, loose clothing that lets sweat evaporate to cool you down.
• Minimize the time you’re outdoors in the hottest hours of the day.

Even when you’re taking these precautions, listening to your body is key.

“If you’re in the heat and begin to feel tired or like your heart is racing, don’t ignore it,” Crawford advises. “It’s important to get your core body temperature down immediately. That might mean stopping what you’re doing or taking a longer break.”