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Heart Disease Health Center

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Hot Summer Days Can Make Sick People Sicker

Extreme heat can affect anyone, but you don't have to become a victim.


The body reacts to heat in many other, less obvious ways. For instance, hot temperatures make your heart beat faster. That's not only if you're exercising. Even if you're sitting perfectly still, your heart will be beating harder when you're hot. That's because the heart is working harder to push blood to the skin and muscles. Getting blood closer to the surface of the body gets it to cool down and helps with sweating.

While this system works pretty well in a healthy person, it may not work so well in people with chronic illnesses.

"Anything that interferes with our natural cooling system could lead us to heat exhaustion and heat stroke faster," McGeehin tells WebMD. "A lot of medical conditions can do that."

When the body can't get rid of excess heat fast enough, the cooling system eventually breaks down, and the organs begin to overheat. If they get hot enough, they'll stop working. Confusion, seizures, permanent disability, and even death can occur if treatment isn't provided. That's heat stroke and it's a medical emergency.

Medical Conditions and Heat Stroke

A number of common health conditions raise the risk of heat stroke including:

  • Heart disease. One of body's responses to heat is to make the heart beat faster. But in many people with heart disease, the damaged heart may not be able to pick up the pace. If the heart can't beat quickly enough, your body won't be able to cool off as well.

    People with heart conditions sometimes take medications called diuretics commonly known as water pills -- which reduce the amount of fluid in the body. When people take water pills, they may become dehydrated easily. The typical advice for people in hot weather "to drink lots of fluids" may not be all that safe for people with heart failure, whose hearts have difficulty handling excess fluid. This can result in backup of fluid in the lungs which can impair breathing.

    Other drugs that are sometimes used for heart problems, such as beta-blockers, can also cause problems. Beta-blockers (such as Toprol, Tenormin, and Lopressor) can prevent the heart from beating as quickly as it needs to during hot weather. This can prevent the body's natural cooling system from lowering the body temperature.
  • High blood pressure. "Hypertension affects the body's ability to keep itself cool," says McGeehin. "It also places greater stress on the heart." In addition, many people with hypertension are on low-salt diets. Not having enough salt in the system can lower the threshold to heat stroke.
  • Diabetes. People with diabetes can be dehydrated when their blood sugars are not under control, says Knochel, and dehydration can prevent the body from sweating normally. Unfortunately, many people with diabetes may not even be aware that they're dehydrated and don't take extra precautions.
  • Obesity. Doctors have come to recognize that obesity is a serious health problem in America. It poses a number of risks, including an increased danger of having a heat-related illness. Part of the problem is simple physics. The bigger the person, the harder it is to lose excess heat. The body's natural cooling systems can't work quickly enough. Obesity also puts extra pressure on the heart, so when hot weather requires that the heart beats even harder, it may not be up to the task, Knochel says.

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