The arctic blast that brought tundralike temperatures to much of the country this winter has left behind more than frozen pipes and frost-nipped noses. During a typical winter, there are up to 36% more circulatory-related deaths than during warmer months.

And it’s not just cold weather that puts you at risk. Researchers have identified other types of weather—throughout the year—that trigger spikes in hospitalizations and death.

For details on the effects that weather can have on your heart, Bottom Line/Healthspoke to Barry A. Franklin, PhD, a leading expert in cardiac rehabilitation.

We hear a lot about cold weather being hard on the heart. At what temperature does this really become an issue? When it’s cold enough to wear a winter jacket, it is cold enough to think about the health of your heart. In fact, research that was recently presented at the European Society of Cardiology Congress 2013 shows that the risk of having a heart attack increases by 7% for every 18°F drop below 73°F.

Why exactly is cold weather so dangerous? Cold temperatures cause blood vessels throughout the body to temporarily constrict, raising blood pressure. Since the arteries that supply the heart are only about the thickness of cooked spaghetti, even a slight narrowing can cause reduced blood flow.

Winter temperatures aren’t generally a problem if you are young and active. But risk rises as you hit middle age and beyond. The risk is highest for adults who are ages 65 and older, particularly those with underlying health problems, such as diabetes, obesity or preexisting heart disease. For people in these groups, spending even a few minutes in below-freezing temperatures can trigger a 20- to 50-point rise in blood pressure.

That’s why I advise older adults, in particular, to stay indoors on the coldest days if possible. When you do go outdoors, don’t depend on a light jacket—you should really bundle up by wearing a hat and gloves and dressing in multiple loose layers under your coat. Each layer traps air that’s been heated by the body and serves as insulation.

And what about hot weather—does it harm the heart? Actually, heat kills more people every year than any other type of weather.

High temperatures, generally above 80°F, but especially greater than 90°F, can cause heat syncope (sudden dizziness and/or fainting)…heat edema (swelling in the feet/ankles)…and heat stroke, in which the body’s core temperature can rise above 104°F. People with atrial fibrillation or dementia are at a 6% to 8% increased risk of dying on hot days. Dementia affects the brain’s ability to regulate the body’s heat response.

Why is strenuous exertion so dangerous for many people during weather extremes? Snow shoveling provides a good example. This activity creates a “perfect storm” of demands on the heart. With snow shoveling, the real danger—particularly for those who are older and/or sedentary—is the exertion itself.

Moving snow is hard work. Each shovelful weighs about 16 pounds (including the weight of the shovel). If you lift the shovel once every five seconds and continue for 10 minutes, you’ll have moved nearly one ton of snow. This exertion can have adverse effects on the heart.

Here’s why: Snow shoveling involves isometric exercise and unaccustomed muscle tension, which increases heart rate and blood pressure. Your legs may stay “planted” when you shovel, which allows blood to pool and reduces circulation to the heart.

Also, people tend to hold their breath (this is known as a Valsalva maneuver, and it often occurs when people are straining to lift heavy loads) when they are wielding a shovel, which causes a further rise in heart rate and blood pressure. That’s why every year, we read or hear about people who dropped dead while shoveling snow.

Is there any way to reduce the risk associated with snow shoveling? If you have or suspect you have heart disease, I suggest that you don’t shovel your own snow. Hire someone to do it for you.

If you are in good shape and want to shovel your own snow, it may be safer in the afternoon. In general, most heart attacks occur between —-6 am and 10 am, when heart rate and blood pressure tend to be higher. You’re also more likely to form blood clots early in the day.

Then be sure to shovel slowly…work for only a few minutes at a time…and keep your legs moving to circulate blood. And remember, it’s best to push snow rather than lift it. This helps keep your legs moving and takes less exertion than lifting. There are snow shovels designed for pushing snow.

What types of exertion are especially dangerous during hot weather? Racket sports, water skiing, marathon running and certain highly competitive sports seem to be associated with a greater incidence of cardiac events in hot, humid weather. Why? Heart rates are disproportionately increased. Electrolytes, such as sodium and potassium, also are lost, which can lead to dangerous heart rhythms.

What steps should people take to protect themselves in hot weather? Everyone knows to drink water when it’s hot. But even people who are consciously trying to stay hydrated often do not drink enough. Drink plenty of cool liquids before, duringand after heat exposure. If you’re sweating a lot, you might want to drink an electrolyte-rich sports drink such as Gatorade or Powerade. And be sure to wear lightweight, loose-fitting clothing when you go outdoors.

In addition, think about any medications you may be taking. Many common drugs, including certain antihistamines and antidepressants, have anticholinergic effects—they inhibit your body’s ability to cool off.

To help your body adapt to heat and humidity: As the weather grows hotter, gradually increase your daily exposure to the heat. The body’s circulation and cooling efficiency increases, generally in eight to 14 days. Afterward, the body is better able to cope with extremes in heat and humidity.