Dr. Roberto Martín Reyes warns that high temperatures destabilize cardiovascular patients and increase the risk of cardiac events, especially in the elderly and people with chronic diseases.
Heat waves are no longer just a one-off summer phenomenon, but an increasingly frequent and prolonged event that poses a growing risk to cardiovascular health. High temperatures, especially when they exceed 35°C during the day and remain above 25°C at night for several consecutive days, increase the risk of myocardial infarction, heart failure , and arrhythmias, particularly in older adults and patients with pre-existing cardiovascular conditions.
Extreme heat has ceased to be merely a meteorological phenomenon and has become one of the main threats to public health. In the last decade, it has caused more than 27.500 deaths in Spain, a figure higher than that recorded for traffic accidents in the same period. During the summer of 2025 alone, approximately one in three days was under officially declared heatwave conditions, a trend that reflects the growing impact of climate change on health, according to data from the Daily Mortality Monitoring System (MoMo) – Carlos III Health Institute.
“Most cardiovascular patients don’t die from heatstroke itself, but rather because the heat acts as a trigger that disrupts an already fragile balance and precipitates a heart attack, stroke, or decompensation of heart failure,” explains Dr. Roberto Martín Reyes, head of the Cardiology Department at La Luz University Hospital. “The heart has to work harder to maintain body temperature, and in vulnerable patients, this extra effort can trigger very serious complications.”
The specialist warns that extreme heat places a significant strain on the cardiovascular system. Vasodilation, fluid loss, and dehydration force the heart to work harder to maintain blood pressure and body temperature, a situation that can destabilize patients with pre-existing cardiovascular conditions.
"Older people, patients with heart failure, hypertension, or a history of coronary artery disease are especially vulnerable during heat waves. During these periods, the risk of myocardial infarction, heart failure, and arrhythmias increases, making prevention essential," the specialist points out.
The haze also affects the heart
The impact of high temperatures is often compounded by the presence of haze and suspended pollutants. These microparticles, in addition to aggravating respiratory illnesses, can also affect the cardiovascular system.
"Small particles can pass through the lungs and reach the bloodstream, promoting inflammatory processes that worsen existing cardiovascular pathologies and increase the risk of complications," explains Dr. Martín Reyes.
Hydration and avoiding the midday hours are key to preventing complications
Experts remind us that proper hydration is the primary preventative measure. It is recommended to drink at least 1.5 liters of water a day, even if you don't feel thirsty.
"With age, the perception of thirst decreases, which means that many older people become dehydrated without realizing it. It's important to drink water regularly throughout the day and not wait until you feel thirsty," emphasizes the head of the Cardiology Department at La Luz University Hospital.
It is also advisable to avoid outdoor physical activity between 12:00 and 20:00, to stay in air-conditioned or well-ventilated spaces and to maintain an ambient temperature close to 24-26º C.
Special caution with certain treatments
People taking diuretics or other medications to control high blood pressure should take extra precautions during heat waves. The combination of vasodilation and fluid loss can cause significant drops in blood pressure.
"In some patients, it may be necessary to temporarily adjust the medication, but this should never be done on your own initiative. Any modification of the treatment should always be carried out under medical supervision," insists Dr. Martín Reyes.
Sport is best done first thing in the morning or last thing at night.
The risk doesn't only affect older people or those with chronic illnesses. Intense physical exercise during the hottest hours of the day can also trigger cardiovascular problems, even in young and healthy people.
"Doing sports during the middle of the day during a heat wave poses an unnecessary risk. It's advisable to move physical activity to early morning or evening, when temperatures are much safer," he explains.
The cardiologist points out that climate change is altering the cardiovascular risk profile of the population. "Heat stress is set to become one of the major cardiovascular risk factors in the coming years. We're no longer talking about isolated incidents, but rather prolonged periods of intense heat that occupy a large part of the summer, and against which we must learn to protect ourselves."
And it concludes with a message of awareness: “We must stop considering heat waves as solely an environmental problem. They are a major health and cardiovascular issue. Just as we protect the population from the cold or pollution, we must learn to protect ourselves from extreme heat, especially those with cardiovascular diseases. Prevention can avoid many complications and save lives.”