The summer months are when you typically gather with family and friends to enjoy cookouts, outdoor concerts, softball games and other activities.
It’s also the time when the summer heat and humidity can affect your health, particularly your heart health.
Does heat raise blood pressure and other cardiovascular risks? Potentially.
Simply put, high temperatures and high humidity can be a dangerous combination for people with cardiovascular disease (CVD).
“Heat and humidity stress the cardiovascular system, exacerbating CVD. People with CVD should be careful about how much time they spend in extreme heat,” says Cleveland Clinic preventive cardiologist Ashish Sarraju, MD. “Anyone with CVD, especially those who are older, is at increased risk of heat-related issues, which could include a heart attack, harmful fluid and electrolyte losses leading to an arrhythmia, or changes in blood pressure.”
Dangerous Conditions
The term “extreme heat” is subjective, so there is no absolute temperature at which danger to the cardiovascular system begins. As a rule of thumb, individuals with CVD should take care in ambient temperatures above 90 degrees Fahrenheit.
“However, the danger point really depends on what temperatures and conditions your body is used to,” Dr. Sarraju says.
For example, if you live in a moderate climate where summer temperatures tend to hover in the 70s, an 80-degree day could pose a risk. Similarly, if your body is acclimated to the tropics, a humid 90-degree day may or may not pose an exceptional risk.
Does Heat Increase Heart Rate?
Perspiration is your body’s cooling response. When you are exposed to unusually hot or humid weather, your body directs blood toward the skin. Because your blood is 90% water, this water appears as sweat. As sweat evaporates, you feel cooler.
Unless the fluid you lose through sweating is replaced, you can become dehydrated. Your blood volume will drop. As you lose electrolytes, your heart rate may increase.
Heat causes blood vessels to dilate, so blood pressure decreases. This process forces the heart to pump faster and work harder, and it also may increase the blood’s tendency to clot. If blood pressure drops lower than it should due to dehydration, your body attempts to correct it by releasing vasopressin, a hormone that helps your body retain water and increase blood volume. It also can cause your blood vessels to constrict, which increases blood pressure. This can be a concern especially if you have hypertension.
High humidity can interfere with the body’s attempts to cool down by preventing sweat from evaporating, leading to a potentially dangerous situation for anyone with heart disease.
Heat, Heart Attack and Stroke
Several studies have found a direct connection between high temperatures, heart attack, and stroke. In 2019, European scientists noticed an increase in the risk of heat-induced heart attack that paralleled rising temperatures caused by global warming.
The same year, Chinese researchers found the risk of heart attack to be 18% higher during two-day heat waves and 24% higher when heat waves lasted four days. When the heat waves caused heavy air pollution, the risk doubled. Women of all ages and adults of both sexes ages 80 and over were the most vulnerable.
Then, in 2024, researchers noted the incidence of stroke increased when temperatures reached 92 degrees and continued to rise as the temperature climbed.
Heart Medications May Add to Risk
Diuretics and beta-blockers—common medications for people with heart disease—can intensify the body’s response to heat.
“Diuretics are designed to eliminate excess water and sodium, so they can worsen fluid losses that occur when you get hot,” Dr. Sarraju explains. “The loss of excess fluid along with sodium and electrolytes can affect the body and blood pressure.
“When blood pressure drops, the body tries to raise it and improve circulation by increasing the heart rate and heart pumping function. Beta-blockers can counteract this effort by preventing the heart from compensating by pumping harder and faster,” he says.
Prepare Yourself for the Heat
If you can’t stay indoors where it is air conditioned, the following measures will help you stay safe when outdoor temperatures and humidity rise:
- Limit or delay outside activity during the hottest hours. Plan your outdoor activities when the temperature and/or humidity are lowest, usually in the early morning, around sunset and after dark.
- Carry cool water with you and stay well hydrated by sipping it often. “Water is the best choice, but sports drinks and electrolyte drinks like Gatorade and Pedialyte are also good options, particularly if you are sweating,” Dr. Sarraju says.
- Avoid caffeine and alcohol, which contribute to dehydration.
- Dress for the heat in loose, lightweight, light-colored clothes made of breathable, natural fabrics.
- Wear a hat when you are outside.
- Wear sunscreen: It will keep you cooler.
Signs of Heat Exhaustion/Heat Stroke
A body that overheats will exhibit the signs and symptoms of heat exhaustion, which include:
- Rapid pulse
- Cool, moist skin
- Profuse sweating
- Dizziness or lightheadedness
- Excessive fatigue
- Nausea
- Headache
- Muscle cramps
If you experience these symptoms, stop what you are doing immediately, move into air conditioning, drink cold water, and cool down by taking a cold shower or using cold compresses. If you don’t feel better in one hour, call 911.
- Heat exhaustion can quickly become heat stroke, which can be fatal. These are the symptoms:
- Hot, dry skin without sweating
- Disorientation
- Confusion
- Agitation
- Inability to drink
- Loss of consciousness
- High fever
If you experience any of these, call 911 immediately.
