The Heat Is on Your Heart, Too

Your heart works overtime to cope with the hot weather

woman outside sweating with towel

We all know the winter and shoveling snow can be dangerous for our hearts. But summer heat — especially during exercise — can be hard on the heart too.

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How the heat makes demands on the heart

David Frid, MD, a cardiologist at Cleveland Clinic, says your heart works harder in the heat, when you’re trying to cool down.

“Your body needs to get rid of excess heat,” says Dr. Frid. “The way it does that is by dilating peripherally. Your blood vessels open peripherally in the outside and you sweat.”

“To be able to get the blood around there your heart works harder,” he says. “The demands are much greater during the hot weather.”

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Exercise adds to heart stress

The load on the heart increases with activity and exercise, especially in hot weather. As the heart works you sweat and, for every degree the body’s internal temperature rises, the heart beats about 10 beats per minute faster.

So when you add exercise to the heat — and to your body trying to cool down — the result is a dramatic increase of stress on your heart.

Keep your heart cool while you exercise

Gordon Blackburn, PhD, is Director of Cardiac Rehabilitation in the Preventive Cardiology and Rehabilitation Program at Cleveland Clinic. He recommends exercising in the cooler morning or evening hours to minimize thermal stress, as well as these other tips for safer hot weather exercise:

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  • Slow down on hot, humid days. Reduce your exercise pace on hot days with high humidity. If the temp is above 80 degrees and humidity above 80 percent, it’s best to postpone your activity until it cools off.
  • Keep extra-hydrated if exercising more than 30 minutes. Drink 8 to 12 ounces of water 20 to 30 minutes prior to exercise, plus 6 to 12 ounces more every 30 minutes of exercise to prevent dehydration.
  • Wear heat-appropriate clothing. Don’t wear items like rubber suits or long-sleeved sweat-suits that prevent evaporation of sweat and interfere with the body’s ability to cool itself. Wear loose-fitting cotton T-shirts, shorts and a brimmed hat while exercising outside.

Take caution even for normal activities

Dr. Frid says take precautions even if you’re simply out in the sun for an extended period.

“If you’re in the heat and begin to feel fatigue or your heart rate going up, find some shade or go indoors for air conditioning and stay hydrated,” says Dr. Frid. “It’s important to work to get your core body temperature down.”

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