Heat waves are not just making you tired: They could be damaging your heart too, doctor warns

Summer in India has started feeling different in recent years. The heat no longer feels like just a seasonal inconvenience. Streets remain hot long after sunset, fans seem useless during humid nights, and stepping outdoors in the afternoon can feel physically exhausting within minutes. But beyond the discomfort, doctors are warning about something far more serious: the silent strain extreme heat places on the heart.

According to the India Meteorological Department (IMD), heat waves in India have become more frequent and intense over the past decade. Health experts now consider extreme heat a growing public health emergency. The heart, which already works non-stop to keep the body functioning, suddenly has to work much harder during periods of severe heat and humidity.

A government-backed study published by the National Institutes of Health (NIH) found that exposure to extreme heat is associated with increased cardiovascular stress and higher risks of heart-related complications, especially among older adults and people with pre-existing illnesses.

Most people think sweating is the body’s only response to heat. In reality, the cardiovascular system immediately goes into adjustment mode.

When temperatures rise sharply, blood vessels expand so heat can escape through the skin. The heart then pumps faster to maintain blood flow and regulate body temperature. This process may sound normal, but during prolonged heat exposure, it becomes physically demanding.

Dr Manish Bansal, Senior Director, Clinical & Preventive Cardiology, Medanta - Gurugram, explains, “When the body is subjected to extreme heat, it tries to cool itself by expanding blood vessels and increasing perspiration. The heart also has to do more work to maintain circulation and control body temperature. This additional work may be responsible for chest pain and irregular heartbeats or worsening pre-existing heart conditions.”

For someone already living with hypertension or coronary artery disease, this extra strain can quietly push the body toward danger. Even healthy individuals may notice pounding heartbeats, unusual fatigue, or breathlessness during extreme heat.

The Centers for Disease Control and Prevention (CDC) also warns that high temperatures increase stress on the cardiovascular system because the body continuously attempts to cool itself.

One of the most underestimated effects of a heat wave is dehydration. Many people wait until they feel thirsty before drinking water, but by then the body may already be struggling.

Heavy sweating reduces blood volume. As fluid levels drop, the heart must pump harder to circulate oxygen and nutrients properly. Blood pressure can fluctuate rapidly, causing dizziness, weakness, headaches, and in severe cases, fainting.

Dr Bansal says, “Prolonged exposure to heat may be accompanied by extreme sweating which leads to loss of fluids and vital electrolytes. Dehydration decreases blood volume, causing fluctuations in blood pressure and making the heart work harder.”

What makes this particularly dangerous is how subtle dehydration can feel in the beginning. Many older adults do not feel thirsty even when their body needs fluids urgently. Diabetic patients and people taking blood pressure medications may also lose fluids faster.

Water loss is only one part of the problem. Sweat also removes important minerals such as sodium and potassium, both of which help regulate heartbeat and muscle function.

Once these electrolytes become imbalanced, the electrical signals that control the heart may get disrupted. That is why some people experience heart palpitations, skipped beats, muscle cramps, or unusual weakness during intense heat.

Dr Bansal explains, “Sweating causes you to lose not only water but also essential electrolytes such as sodium and potassium. When there is a large imbalance of these minerals, you may experience an increase in frequency or type of heart palpitations or an increased risk for developing other cardiac rhythm disturbances.”

This becomes more serious in people taking diuretics or certain cardiac medications, since these medicines already affect fluid balance in the body.

Heat stroke is not simply “feeling too hot.” It is a medical emergency where the body loses its ability to cool itself.

Once body temperature rises uncontrollably, organs begin to suffer. The heart, brain, and kidneys are among the first to feel the impact.

Symptoms begin quietly: rapid heartbeat, confusion, nausea, severe fatigue, chest discomfort, or shortness of breath. But within minutes, the condition can become life-threatening.

Dr Bansal warns, “If the body struggles to cool down, heat exhaustion and heat stroke may occur, both of which can cause severe damage to the heart.”

​Research published by the National Library of Medicine explains that heat stroke can trigger inflammation, abnormal clotting, and cardiac stress that may permanently damage organs if treatment is delayed.

Many people ignore early warning signs because they assume they are simply “tired from the heat.” That delay can become dangerous.

Heat waves do not affect everyone equally. People living with heart disease usually face higher risks during prolonged heat exposure.

Conditions such as heart failure, hypertension, previous heart attacks, and coronary artery disease make it harder for the body to adjust to sudden temperature changes.

Dr Bansal notes, “People who suffer from heart diseases, such as hypertension, heart failure, and coronary artery disease, as well as those who have had previous incidents of heart attacks, face more severe symptoms during heat wave.”

Even excessive water intake can become risky for some cardiac patients because fluid overload may stress the heart further. That is why doctors often recommend personalised hydration plans for people with chronic heart conditions.

Protecting the heart during a heat wave does not always require complicated measures. Often, simple habits make the biggest difference.

Avoid direct sun exposure between noon and 4 pm when temperatures peak. Wear loose cotton clothing that allows sweat to evaporate. Eat lighter meals during extremely hot days because digestion itself generates body heat.

People who work outdoors should not ignore short breaks in shaded or cooler spaces. Families should also check regularly on elderly relatives, especially those living alone.

Dr Bansal advises, “People with existing heart conditions should not skip medications and consult their doctor if they notice symptoms such as chest pain, palpitations, unusual breathlessness, or excessive fatigue.”

The body usually whispers before it screams. Heat-related heart stress often begins with small warning signs that are easy to dismiss.

This article includes expert inputs shared with TOI Health by:

Dr Manish Bansal, Senior Director, Clinical & Preventive Cardiology, Medanta - Gurugram.

Inputs were used to explain how rising temperatures and prolonged heat exposure can place extra stress on the heart, worsen existing cardiovascular conditions, and why recognising early warning signs during heat waves is crucial for staying safe.