So this tool is known as an electrocardiogram. An electrocardiogram is a graph that describes the electrical signal that is generated by the heart. Now, how do we actually obtain the electrocardiogram? Well, we basically take special electrodes and we connect the electrodes onto the surface of the skin as special locations on the body. So six electrodes are usually placed around the heart. Two electrodes are placed on the arms and two electrodes are placed on the legs.