The snow in the driveway might need clearing, but if you have any kind of heart condition then you shouldn’t be the one to do it. That’s because the combination of physical exertion, sub-zero temperatures and a poor heart can lead to serious medical problems. Medical experts generally advise anyone being treated for a heart illness against pushing themselves too heard when temperatures dip below zero. What happens is that the blood vessels in the body contract when it is very cold. The puts a strain on the heart as it has to pump the blood through the veins against greater resistance, explains…