Excessive air conditioning turns heart attacks into a summer disease

As temperatures climb, air conditioning use is rising — and with another severe heat wave forecast for this year, a surprising seasonal pattern in heart attacks is drawing attention. Acute myocardial infarction, commonly associated with cold weather, actually strikes middle-aged and older adults more frequently in summer.

Data from the Health Insurance Review and Assessment Service covering December 2020 through August 2025 show that hospital visits for acute myocardial infarction were higher in summer (June–August) than in winter (December–February). Over the five-year period, summer cases totaled 502,086 — more than 13,500 above the winter figure of 488,506. Men accounted for roughly 80 percent of all patients, with men in their 60s representing the largest group.

Acute myocardial infarction is a severe cardiac emergency in which a coronary artery supplying blood to the heart muscle is suddenly blocked by a blood clot, causing the muscle tissue to die. The condition develops when cholesterol deposits and inflammation accumulate on artery walls, forming atherosclerotic plaques. When a plaque ruptures, a clot forms and obstructs the coronary artery.

Two key summer triggers are dehydration and excessive air conditioning. Heavy sweating rapidly depletes the body's fluids, thickening the blood and creating conditions favorable to clot formation. Aggressive air conditioning poses a separate risk: moving abruptly from sweltering outdoor heat above 30 degrees Celsius into a heavily cooled room causes blood vessels — dilated to release body heat — to constrict almost instantly. That sudden constriction sharply increases pressure on the heart and can make atherosclerotic plaques more prone to rupture. Experts recommend keeping the gap between indoor and outdoor temperatures to around 5 degrees Celsius and carrying a light outer layer to buffer rapid changes in body temperature.

The hallmark warning sign is severe chest pain unlike anything the patient has felt before — often described as a tearing sensation or the feeling of being crushed — that does not ease with rest after 30 minutes or more. The pain may radiate to the inner left arm or the jaw and can be accompanied by cold sweats.

Older adults and people with diabetes may experience a "silent" heart attack with no chest pain at all. In such cases, sudden shortness of breath, extreme fatigue, cold sweats, nausea, or a heavy feeling in the upper abdomen may be the only signs. An electrocardiogram and blood tests are needed for an accurate diagnosis.

In treatment, securing the golden hour is critical. Drug therapy using thrombolytics to dissolve the clot is an option, but directly reopening the blocked vessel is more effective when possible. Percutaneous coronary intervention — which uses a balloon or metal mesh stent to widen the artery — is the standard procedure, and the blocked vessel generally must be reopened within two hours to minimize damage to the heart muscle.

"Survival rates and outcomes after acute myocardial infarction depend heavily on how quickly the blocked vessel can be reopened," said Lim Sang-yeob, a professor of cardiology at Korea University Ansan Hospital. "Patients must receive a rapid diagnosis in the emergency room immediately after symptoms appear, and if necessary, undergo percutaneous coronary intervention without delay." He added that middle-aged and older adults with underlying conditions such as hypertension, diabetes or hyperlipidemia, or those who smoke, should avoid strenuous outdoor activity during heat waves.

By Kim Tae-yeol, senior reporter