If you have ever shoveled snow you can imagine how someone with a bad heart might die from shoveling snow too fast. Suppose we have two identical twins, aged 54, with equally bad hearts. Suppose the first twin goes out to shovel his driveway which has a foot of heavy damp snow. Suppose he starts out fast, works too hard and has a heart attack. Suppose the second twin has an identical situation, a driveway which has a foot of heavy damp snow. Suppose our second twin starts out very slow, and very slowly, say over a period of say thirty minutes (it's a long drive way) gradually increases his effort, slowly working harder and harder. Because this twin gradually increases his effort will he likely have any warning that his sick heart is working too hard? Is he more likely to avoid a heart attack because he started out slow? I wonder if a strategy of starting out slowly with any intense physical activity and slowly increasing your effort can reduce the risk of heart attack? Conversely is there a way a person with a sick heart can guarantee killing them selves with intense physical activity? Thanks for any help!