Exposure to heat was found to stress the heart of adults by increasing the blood flow to the organ's walls, according to a new study.

The researchers also found evidence of obstructed blood flow induced because of the heat in some of the adult participants with heart disease, even though they did not display symptoms externally.

The researchers, including those from Canada’s Montreal Heart Institute, said these adults may benefit by staying cool to counter the heat's stress on their hearts.

For the study, published in the journal Annals of Internal Medicine, the team recruited 61 adults -- 20 healthy young adults, 21 healthy older adults and 20 older adults with coronary artery disease (CAD) -- to see how exposure to extreme heat impacted the heart.

CAD is a condition in which blood vessels supplying to the heart are narrowed because of plaque buildup, thereby limiting blood flow.

The researchers artificially raised the core body temperature of the participants by 1.5 degrees Celsius and measured their myocardial blood flow (MBF) - blood reaching muscles of the heart wall - before exposure and also at every increase of 0.5 degrees Celsius to their core temperature.

The authors found that blood flow to the heart muscles increased in all participants when their body temperature increased by 1.5 degrees Celsius.

Using imaging techniques, the authors further observed that seven of the participants with CAD experienced heat-induced myocardial ischemia in which blood flow to the heart is obstructed due to blockage in vessels. The participants, however, did not outwardly show symptoms of the condition.

In an accompanying editorial from Annals of Internal Medicine and the University of Pennsylvania Perelman School of Medicine (US), the researchers said that exposure to heat can significantly stress the heart by inducing a supply-demand mismatch in vessels.

With temperatures around the world on the rise, identifying vulnerable people with conditions of the heart and blood vessels is imperative, it said.

Repeated exposures can result in a "symptomatic or silent" blood flow problems, which could partly explain the increased risk for adverse cardiovascular events observed because of heat exposure in population studies, it said.

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