I really haven't given much thought to the risks of shoveling snow, I usually grab the shovel and head out and move the white stuff off the walkway's and driveway.  Then I heard about a friend who was in the hospital after suffering a 'heart attack' while shoveling his driveway. When I did a little more research into this I found that if you are not in the best of health you may not want to pick up the shovel and start moving the snow.  According to the American Heart Association, shoveling snow can be strenuous and certain people should never pick up a shovel.  If you have coronary artery disease you could trigger a heart attack if you start shoveling snow, it's hard work.  Additionally a heart attack can be triggered by extremely cold temperatures, it can cause artery's to tighten and increase blood pressure. If you are at risk of this get someone else to do the shoveling for you, if you don't think you are at risk and you find yourself short of breath, feel some chest pain and discomfort in your left arm, put the shovel down and seek medical attention.

Here is more shoveling advice from the National Safety Council:  http://www.nsc.org/news_resources/Resources/Documents/Snow_Shoveling.pdf