When sedentary people suddenly find themselves shoveling show, bad things can happen. Every winter, there is a news item about someone who had a heart attack while shoveling snow. But even active athletes might be at risk, because there’s an additional and very important connection between shoveling snow and having a heart attack. Few folks are aware of that interaction, because most don’t know what happens inside their body when they are outside in cold weather.

Two years ago, the Harvard Health Blog published an article by Patrick J. Skerrett in which he states, “Snow shoveling is a known trigger for heart attacks. Emergency rooms in the snowbelt gear up for extra cases when enough of the white stuff has fallen to force folks out of their homes armed with shovels or snowblowers.”

Cold weather causes blood vessels to contract, making them narrower. That restricts blood flow, which in turn lowers the amount of oxygen your heart receives. In order to get the extra oxygen the heart requires when doing something strenuous, it must pump harder to get blood flowing faster while you shovel snow. That makes your heart rate increase, just as your heart beats faster when running a sprint or pedaling a bike at full speed up a steep hill. So not only does your heart work harder, but your blood pressure goes up as well.

Here are basic tips to prevent a heart attack when shoveling snow:

First, drink a large glass of water before you start. You may not feel yourself sweating in cold weather, but the fact is that strenuous work will always make you sweat, no matter what the temperature is outside, and you don’t want to be dehydrated while doing hard, physical work.

Also remember that the job of clearing snow involves a lot of twisting. Warm up the muscles used in that motion (obliques and spinal erectors) before you go out and start making that move with the additional weight of a shovel full of snow.

When you leave your warm home to go out into the cold, your body warmth will last for a while. Once your body begins to adjust to the outdoor temperature, that’s when your blood vessels will react. A good way to keep your interior warm is the “five-minute span.” Shovel snow for five minutes, then go inside for five minutes, or even longer if your feet or fingers began to feel cold outside.

Don’t strain yourself. Skerrett suggests, “Shovel many light loads instead of fewer heavy ones.” That will help keep your heart from working too hard.

Remember that cotton, once it gets wet, will draw off heat from your body, so don’t wear a pair of cotton sweats in the snow. In fact, whether or not you actually ski, go to an inexpensive secondhand shop and pick up a pair of roomy ski pants, which will keep your legs and ankles warm.

And if you have no one to welcome you back inside with a cup of hot chocolate, make one for yourself before you go outside, and warm it up once you’re done.