And that creates a closed electric circuit. And if we connect the wires to a special device, that device can read the electrical signal that is generated by our heart. So we basically create an electrocardiogram that is nothing more than an XY graph, where the X axis is the time and the Y axis is the voltage. So we see that the electrocardiogram is the fluctuations, the change in voltage that is produced by the heart. And this voltage is used to basically generate that muscular contraction that propels all that blood through the blood vessels of our body. Now, in this lecture, we're going to study the normal electrocardiogram.