In cariology, a wandering pacemaker is an atrial arrhythmia that occurs when the natural cardiac pacemaker site shifts between the SA node, the atria, and/or the AV node. This shifting of the pacemaker from the SA node to adjacent tissues is manifested electrocardiographically by transient changes in the size shape and direction of the P waves. A wandering pacemaker is usually caused by varying vagal tone. With increased vagal tone the SA Node slows,allowing a pacemaker in the atria or AV Nodal area,which may become slightly faster briefly. After vagal tone decreases the SA Node assumes pacemaker.