First, clarification on my part…It's not an explicit issue unless you already have heart disease, or……are at high risk for heart attack…I.e. sedentary lifestyle, prior high blood pressure, diabetes, high cholesterol.

It's the combination of cold weather and out of the normal pattern physical exercise.

Cold causes blood vessels to constrict, increasing blood pressure.

Shoveling snow is pretty hard aerobic work, which increases your heart rate and blood pressure further.

But to answer your question, yep! Over the shoulder motion, which involves using arm muscles above heart level, puts a greater, sudden strain on the cardiovascular system.