Shoveling snow does not cause heart attacks in most healthy people.
However if you already have a heart condition, have suffered from heart attacks before or have heart disease then shoveling snow could lead to a heart attack.
Shoveling snow is hard work and strains your body and your heart as well so when you have other health issues and your heart is not healthy then you could have a heart attack.
Now if you were out shoveling snow for hours and hours without a break then the over exertion from shoveling snow can cause you to have a heart attack.
It's rare though to have a heart attack when shoveling snow and most people who do have heart attacks while shoveling snow have the heart attack because they over exerted themselves or they already have heart issues.
I've shoveled snow many times and so far have never had any heart attacks and I also take breaks while shoveling the snow.
I have a neighbor who is 90 years old and he shovels snow every year and has not had a heart attack either.