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Home / Blog / Heat and the Heart

Heat and the Heart 08.07.2026

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Heat Is More Than Just Uncomfortable: What Happens to the Heart and Blood Vessels on Hot Summer Days?

High summer temperatures place significant strain on the body. They affect blood circulation, fluid balance and the way the heart functions. A healthy person can gradually adapt to heat, but in people with cardiovascular disease, diabetes or kidney disease, high temperatures can worsen their condition.

A study published in Nature Medicine in 2025 estimated that approximately 62,775 deaths in Europe during the summer of 2024 were associated with high temperatures. This is not the number of directly recorded heat-related deaths, but a statistical estimate of mortality attributable to heat.

“Hot weather places more strain on the heart than many people realise. The body has to maintain a stable core temperature, which increases the demands placed on both the circulatory system and the heart,” explains MUDr Marcela Schejbalová, cardiologist at MY CLINIC.

What Happens to the Body in Hot Weather?

The body tries to get rid of excess heat in two main ways.

The blood vessels in the skin dilate. More blood is directed towards the skin, helping the body release heat. At the same time, however, blood pressure may fall and the heart has to work harder and faster to maintain an adequate blood supply to the organs.

Sweating increases. The evaporation of sweat cools the body, but it also leads to the loss of water and electrolytes. If these fluids are not replaced, the volume of circulating blood decreases.
In humid conditions, sweat evaporates less effectively, making it more difficult for the body to cool itself.

Why Does Heat Put Strain on the Heart?

At high temperatures, the heart has to pump more blood towards the skin. When this is combined with dehydration, it can result in a faster heart rate, lower blood pressure and a reduced volume of circulating blood.

Possible consequences include:

  • fluctuations in blood pressure,
  • palpitations or abnormal heart rhythms,
  • worsening of heart failure,
  • inadequate blood supply to the heart muscle,
  • an increased risk of thrombotic complications in high-risk patients.

The combination of heat, physical activity, alcohol and insufficient fluid intake is particularly demanding on the cardiovascular system.

Who Should Be Especially Careful?

People at higher risk include those:

  • with high blood pressure,
  • with coronary artery disease or a history of heart attack,
  • with heart failure,
  • with heart rhythm disorders,
  • with diabetes or kidney disease,
  • living with obesity,
  • of advanced age.

Extra caution is also needed when taking diuretics and certain medicines for high blood pressure.

Never stop taking medication or change the dosage without consulting your doctor. If you repeatedly experience low blood pressure, dizziness or weakness in hot weather, speak to your doctor.

Travelling to Hot or Tropical Destinations

A sudden move to tropical temperatures can place considerable strain on the body. Acclimatisation to heat usually takes several days, so it is advisable to limit strenuous exercise, direct sun exposure and demanding excursions after arrival.

Patients with cardiovascular disease should travel only when their condition is stable and should ensure that they have an adequate supply of their regular medication.

During long journeys by plane, car or coach, it is important to get up regularly, walk around and exercise the calf muscles. Prolonged sitting increases the risk of venous thrombosis, particularly in people with additional risk factors.

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How Can You Tell When Your Body Is Struggling with the Heat?

Warning signs include:

  • a rapid or irregular heartbeat,
  • marked weakness and dizziness,
  • feeling faint,
  • shortness of breath,
  • chest pain or pressure,
  • nausea, confusion or loss of consciousness.

If you experience severe chest pain, significant shortness of breath, speech difficulties, confusion or loss of consciousness, call the emergency medical services immediately – 155 in the Czech Republic or 112 in EU countries. Outside the EU, call the local emergency number.

How Can You Help Your Heart Cope with the Heat?

  • Drink fluids regularly rather than waiting until you feel thirsty.
  • Stay somewhere cool, avoid direct sunlight and use a lukewarm shower to help cool your body.
  • Plan exercise and strenuous work for the morning or evening.
  • Limit alcohol, which can contribute to dehydration.
  • If you are being treated for high blood pressure, monitor your blood pressure and pay attention to any symptoms.

Patients with heart failure or kidney disease may have an individually prescribed fluid restriction. In these cases, the general advice to drink as much as possible does not apply.

“If you repeatedly experience palpitations, significant shortness of breath or fluctuations in blood pressure during hot weather, it is not advisable to simply attribute these symptoms to the temperature. They may indicate an underlying condition that has not yet been diagnosed,” adds MUDr Marcela Schejbalová.

Prepare for Summer and Travel

A cardiological assessment may be worth considering if you have cardiovascular disease, multiple cardiovascular risk factors or repeatedly experience palpitations, shortness of breath, chest pain, dizziness or significant fluctuations in blood pressure during hot weather.
A comprehensive cardiological screening at MY CLINIC can help assess the condition of your heart and blood vessels, identify significant risk factors and establish personalised preventive measures.

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