Second degree AV block is also known as Mobitz type 2. Here, every 2nd, 3rd, or n-th atrial excitation is conducted to the ventricles. In the ventricles, we talk about a 2:1, 3:1, or n:1 conduction. Since the AV node is influenced by the vegetative nervous system, and the sympathetic nerve is positively dromotropic, only a small degree of physical activation is necessary to increase the rate of conduction. So an excitation ratio of 3:1 can suddenly change to a ratio of 2:1. On occasion, the number of transmitted excitations changes several times within the space of a few heart beats.