People who are outdoors in cold weather should avoid sudden exertion, like lifting a heavy shovel full of snow. Even walking through heavy, wet snow or snow drifts can strain a person's heart.

How does cold weather affect the heart?

Many people aren't conditioned to the physical stress of outdoor activities and don't know the dangers of being outdoors in cold weather. Winter sports enthusiasts who don't take certain precautions can suffer accidental hypothermia (hi"po-THER'me-ah).

Hypothermia means the body temperature has fallen below normal. It occurs when your body can't produce enough energy to keep the internal body temperature warm enough. It can kill you. Heart failure causes most deaths in hypothermia.

Symptoms include lack of coordination, mental confusion, slowed reactions, shivering and sleepiness.

Children, the elderly and those with heart disease are at special risk. As people age, their ability to maintain a normal internal body temperature often decreases. Because elderly people seem to be relatively insensitive to moderately cold conditions, they can suffer hypothermia without knowing they're in danger.

People with coronary heart disease often suffer chest pain or discomfort called angina pectoris (AN'jih-nah or an-JI'nah PEK'tor-is) when they're in cold weather. Some studies suggest that harsh winter weather may increase a person's risk of heart attack due to overexertion.

Besides cold temperatures, high winds, snow and rain also can steal body heat. Wind is especially dangerous, because it removes the layer of heated air from around your body.  At 30 degrees Fahrenheit in a 20-mile-per-hour wind, the cooling effect is equal to calm air at four degrees. Similarly, dampness causes the body to lose heat faster than it would at the same temperature in drier conditions.

To keep warm, wear layers of clothing. This traps air between layers, forming a protective insulation. Also, wear a hat or head scarf. Much of your body's heat can be lost through your head.  And ears are especially prone to frostbite. Keep your hands and feet warm, too, as they tend to lose heat rapidly.

Don't drink alcoholic beverages before going outdoors or when outside.  Alcohol gives an initial feeling of warmth, because blood vessels in the skin expand.  Heat is then drawn away from the body's vital organs.