The electrical characteristics of the atrio-ventricular conducting system change throughout its course. In the upper portion of the AV node, the action potentials have a decreased resting potential and slowed rate of rise of the action potential upstroke (less than 10 V/sec). Impulse conduction in this region is slowed to 2-5 cm per second. In the lower portion of the AV node, the action potentials assume characteristics of the common His bundle with more rapid upstroke velocities. In the His bundle, the maximum rate of rise of the action potential upstroke reaches 300 volts per second and conduction velocity approaches 1-3 meters per second.