The livin’ may be easy during summertime, but that’s not the case for your heart. Heat is hard on your cardiovascular system. That’s because your body has to work harder during hot, humid weather to maintain balance. And this puts excess stress on your heart and impedes healthy circulation.
In Traditional Chinese Medicine (TCM), summer is associated with the fire element. On a physical level, this correlates to the health of your heart and circulatory system. As daylight increases, your energy and activity naturally expand, moving farther away from your core. You need strong circulation to keep up with these increased demands.
Poor circulation creates stagnation, and stagnant blood generates heat in the form of inflammation, a factor in all chronic illnesses, including heart disease, Alzheimer’s, and cancer. The combination of sluggish circulation and inflammation also contributes to hyperviscosity, aka thicker blood that flows less easily.
Hyperviscosity is sometimes caused by a genetic mutation — approximately 25 percent of the population exhibits one or more “defects” such as elevated Lp(a) cholesterol, homocysteine, or PAI-1 (a blood-clotting protein). But hyperviscosity can also be caused by lifestyle, dietary habits, infections, or traumas. When both inflammation and hyperviscosity are present, every system in your body, especially your heart, is negatively affected.
Understanding these effects is crucial for everyone, but particularly for those with high blood pressure or heart conditions. (Heat-related hospitalizations increase for people with cardiovascular conditions during hot weather.)
Why Your Heart Works Harder in the Heat
When your body temperature rises, your heart pumps harder and faster to help cool you down. During extreme heat stress, your cardiac output (the amount of blood your heart pumps per minute) can increase from approximately 5 L/min at rest to as high as 13 L/min. This is up to a 2.5-fold increase from normal resting values.1
Your heart rate can rise well over 100 beats per minute during passive heating.2 This occurs through both direct effects of temperature on cardiac cells and changes in your autonomic nervous system activity. Heat speeds up the electrical signals controlling your heartbeat, causing your heart to beat more frequently and with greater force.1
Your heart also has to maintain this increased workload while dealing with less blood flowing back to the heart because it’s being redirected to your skin. Your skin’s blood vessels can dilate significantly (vasodilation), allowing blood flow to increase from approximately 300 mL/min to an astonishing 7,500 mL/min during intense heat exposure. This means that during extreme heat, up to 50% of your cardiac output may be directed to your skin.2
Sweating works with this vascular response. As sweat evaporates from your skin, it pulls heat away from the blood vessels near the surface. However, profuse sweating can lead to dehydration, reducing blood volume and further challenging your cardiovascular system.
Warning: High Blood Pressure and Heat Don’t Mix
If you have hypertension, your risks are even greater during hot weather, especially if you take prescription medications for high blood pressure. Many common hypertension treatments can interfere with your body’s natural cooling mechanisms. Here’s a quick overview:
- Diuretics (water pills): These medications increase urination, leading to fluid loss and potential dehydration, which can impair your body’s ability to sweat and cool down.
- Beta-blockers: These can reduce blood flow to the skin and decrease your heart rate, making it harder for your body to dissipate heat and regulate its temperature.
- ACE Inhibitors: While primarily working to relax blood vessels, ACE inhibitors may also reduce the body’s ability to sweat effectively and can increase the risk of fainting in hot weather due to their blood-pressure-lowering effect.
- Calcium Channel Blockers: These can cause electrolyte imbalances that may interfere with temperature regulation.
Other medications to be cautious with during extreme heat:
- Angiotensin II Receptor Blocker (ARBs like lisinopril, enalapril, losartan) can reduce thirst sensation while lowering blood pressure, increasing dehydration risk during hot weather.
- Antipsychotics and certain antidepressants affect the hypothalamus—your body’s thermostat—potentially impairing temperature regulation and reducing sweating capacity. Tricyclic antidepressants decrease sweating, while some SSRIs may increase it.
- Antihistamines with anticholinergic properties (like diphenhydramine) block signals to sweat glands, reducing your ability to cool down through perspiration.
- Stimulants used for ADHD or weight loss increase metabolic rate and heat production, potentially overwhelming cooling mechanisms in hot weather.
Note: Never stop taking prescribed medications without consulting your healthcare provider. Instead, take extra precautions during hot weather if you’re on these medications, including limiting outdoor exposure, increasing fluid intake, and staying indoors in air-conditioned environments.
Age significantly reduces the body’s ability to sense dehydration and respond to temperature changes. Older adults with hypertension experience diminished thirst sensation yet face greater dehydration risk, creating a dangerous combination.
Obesity compounds these risks through multiple mechanisms. Excess body weight contributes directly to cardiovascular risk factors, including worsening hypertension. Furthermore, obesity increases metabolic heat production while simultaneously reducing the efficiency of heat dissipation through the skin. Studies indicate that obesity accelerates early atherosclerotic changes through several mechanisms, including insulin resistance and inflammation.3
How to Stay Safe During Hot Weather
These strategies can help minimize risks and keep you and your heart safe when the weather heats up.
Stay Indoors During Peak Heat Hours:
Limit your time outdoors between 10 a.m. and 4 p.m., typically the hottest part of the day. That means scheduling any necessary outdoor activities for early morning or evening hours. Adjust your exercise: If you must go outside, wear lightweight, light-colored clothing in breathable fabrics like cotton, and use mineral-based sun protection and a wide-brimmed hat.
Prevent dehydration:
Proper hydration is crucial for heart health during hot weather. Drink water before, during, and after any outdoor activity. (If you have any type of fluid restrictions, consult your physician about potentially adjusting these limits during extreme heat.)
Many of us are chronically dehydrated and don’t know it — dry mouth and thirst are not always present in cases of dehydration. Your urine color is a better gauge; darker-colored urine signals dehydration, while light-yellow or even colorless urine indicates that you are properly hydrated.
Chronic dehydration can lead to electrolyte imbalances, causing vague symptoms often confused with other health issues, such as dizziness, lightheadedness, headache, disorientation, muscle spasms (typically in the abdomen, arms, or legs), stomach cramps, weakness, heavy sweating, nausea or vomiting, and sunken eyes.
Dehydration can also happen when you confuse thirst for hunger. That’s why people often turn to a sugary snack when the body is asking for fluids. Constant snacking — and especially constant sugar cravings — can be a hidden sign of a dehydration imbalance.
Eat more high-water foods:
Take advantage of the increased fresh produce available this time of year, emphasizing leafy greens and hydrating fruits and vegetables with high water and/or mineral content (e.g., melons, strawberries, pineapple, celery, cucumbers, and zucchini). You may also want to replenish electrolytes with a healthy electrolyte and mineral drink or supplement (including electrolyte powder mixes).
Keep Chronic Inflammation in Check:
This is the most important step you can take to protect your health during summer. The degenerative process of continuous “overheating” degrades your body through wear, tear, and oxidative stress, serving as a primary function of the aging process and of degenerative, life-threatening diseases.
Make Time for Meditation:
Research shows that meditation and mindful relaxation practices offer unique heart health advantages.
Schedule That Vacation:
We know from basic physics that heat is a manifestation of an increase in kinetic movement, and when you live a high-paced lifestyle with no time to relax, “cool,” re-hydrate, or lubricate your body, your “engine” is going to heat up. So, take it slow. Go on vacation. Reconnect with friends and family. Read a good book.
Warning Signs of Heat-Related Illness
The body sends clear distress signals before more serious complications develop, giving you valuable time to take protective action.
Dizziness and confusion:
Mental status changes often appear as the first indicators of heat stress. Watch for sudden confusion, altered mental status, or slurred speech, which can signal dangerous overheating. Even mild disorientation or difficulty concentrating warrants immediate attention. These symptoms occur as blood flow shifts away from the brain to cool the body, a particularly dangerous scenario for those with hypertension.
Rapid Heartbeat or Fainting:
Cardiovascular warning signs include a noticeably fast heart rate (tachycardia) and a weak, rapid pulse described as “thready.” Heat syncope—fainting or brief loss of consciousness—happens when standing too long or suddenly rising from sitting. This occurs as blood vessels dilate to release heat, potentially causing dangerous drops in blood pressure. If someone faints in hot weather, move them to shade immediately and seek medical help.
Summer can be an exciting and rewarding season, offering more time in nature, new adventures, an abundance of healthy fresh produce, summer celebrations, and more. If you take the right steps to adjust your routine during this period, you can protect your heart and entire cardiovascular system from heat-induced illness.
References
Alahmad B, Khraishah H, Shakarchi AF, et al. Cardiovascular Mortality and Exposure to Heat in an Inherently Hot Region: Implications for Climate Change. Circulation. 2020 Apr 14;141(15):1271-1273. doi: 10.1161/CIRCULATIONAHA.119.044860. Epub 2020 Mar 30. PMID: 32223316; PMCID: PMC9060422.
2. Crandall CG. Heat stress and baroreflex regulation of blood pressure. Med Sci Sports Exerc. 2008 Dec;40(12):2063-70. doi: 10.1249/MSS.0b013e318180bc98. PMID: 18981943; PMCID: PMC2819365.
3. Powell-Wiley TM, Poirier P, Burke LE, et al. Obesity and Cardiovascular Disease: A Scientific Statement From the American Heart Association. Circulation. 2021 May 25;143(21):e984-e1010. doi: 10.1161/CIR.0000000000000973. Epub 2021 Apr 22. PMID: 33882682; PMCID: PMC8493650.
