You’ve probably heard that shoveling snow can up your risk of a heart attack. Yet falling temperatures can increase the odds you’ll have a heart attack even if you don’t clear a snow-covered driveway or dig out your car.

Here’s what you need to know about this cold-weather heart risk—and how to recognize the signs of a heart attack any time of year.

The Dangers of a 'Cold' Heart

Cold weather can increase blood pressure and raise cholesterol levels—two key risk factors for heart attack. It can also make blood more likely to form heart-threatening clots.

According to one study of 84,010 heart attack patients, every 1.8° F (or 1° C) temperature drop was associated with a 2 percent increase in the risk of having a heart attack. Another study published in 2015 found up to a 31 percent increase in heart attacks in the coldest months of the year compared with the warmest.

Winter weather, studies suggest, may be especially risky for your heart if you’ve already had a heart attack, have heart disease, or are older than 65. (The risk for stroke can rise in winter, too.)

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A number of silent, seasonal cardiovascular changes may explain the uptick. As temperatures drop, your blood vessels tighten and blood flow speeds up to help you stay warm. That’s why your blood pressure is often higher in colder seasons. Cholesterol levels appear to rise in midwinter, too.

Blood levels of immune system compounds that help your body fight off infections are also higher in winter. That might help boost your natural defenses against cold and flu germs, but it may also pack more plaque into artery walls, according to researchers from the Icahn School of Medicine at Mount Sinai in New York.

It’s not clear whether you can control these seasonal shifts. But researchers say your best winter heart-protection strategy is a simple one: Stay warm. Dress in layers and don’t forget a hat and gloves—your sense of how cold you are may diminish as you get older.

That’s especially important when you’re exerting yourself outdoors, shoveling snow, for example. Try some light physical activity—such as running in place—before diving into intense exertion like digging your car out. (If you’re older than 50 and not a regular exerciser, you may want to skip the shoveling altogether.)

In addition, during holiday meals and parties, go easy on high-fat goodies and alcohol, which may contribute to the spike in holiday heart attacks, some experts suspect.

Most important, know that your risk for a heart attack is greater in the winter, and stay alert to the often subtle signs that you might be having one.

Signs of a Heart Attack

Despite the sudden chest pain and collapse usually depicted in movies and TV medical dramas, heart attack can present in a variety of ways, not all of them involving chest pain.

If you’re male, the classic chest pain is indeed the No. 1 symptom of a heart attack (though not the only one). The pain usually lasts for more than a few minutes, or recurs. It’s commonly described as feeling like an elephant is standing on your chest, but it can also feel like discomfort or pressure.

Other symptoms include nausea and vomiting; upper-body pain in the arms, back, shoulders, neck, jaw, or abdomen; shortness of breath; and a feeling of fullness in the center of the chest. 

If you’re female, however, a heart attack can present a little differently, says Karol Watson, M.D., Ph.D., co-director of the UCLA Program in Preventive Cardiology.

“Chest pressure is usually somewhere in the mix,” Watson says, “but it may not be the most prominent symptom.”

Women may come into the doctor’s office with symptoms that don’t evoke a “classic” heart attack: overwhelming fatigue; shortness of breath; nausea; dizziness; sweating; flulike symptoms; and abdominal, jaw, or back pain.

For everyone, the symptoms can be subtle. The risk of having a heart attack but not noticing any symptoms—a phenomenon known as silent heart attack—may be much greater than scientists had previously believed.

A 2016 study published in the journal Circulation showed that as much as 45 percent of heart attacks are silent. And that risk may be especially acute in people who have a higher tolerance for pain, according to a new study out of Norway. That’s why it’s important to stay attuned to any possible signs, even if they’re atypical.

“If you’re going through your usual and regular day, and what’s normal for you suddenly becomes really difficult, you’ve got to think of your heart,” says Suzanne Steinbaum, D.O., national spokeswoman for the American Heart Association’s Go Red For Women campaign.

If you suspect you’re having a heart attack, call 911 immediately. Then chew and swallow one 325-mg uncoated aspirin (or four 81-mg baby aspirins) to help prevent clots from forming in your coronary arteries. Don’t even think about driving to the hospital yourself or having someone take you.