An electrocardiogram is a recording of the small electric waves being generated during heart activity. A normal heart beat is initiated by a small Pulse of electric current. This tiny electric “shock” spreads rapidly in the heart and makes the heart muscle contract. If the whole heart muscle contracted at the same time, there would be no pumping effect. Therefore the electric activity starts at the top of the heart and spreads down, and then up again, causing the heart muscle to contract in an optimal way for pumping blood.