P wave changes suggesting a wandering atrial pacemaker are frequently observed on ambulatory ECG recordings from younger individuals. The ECG strips shown here are from an ambulatory ECG recorded on a 15 year old female. The upper tracing is recorded by electrodes placed so as to simulate lead V5 and the lower, by electrodes placed to simulate lead V1. Note that as the P-P intervals change in a phasic fashion, indicating sinus arrhythmia, there is a change in P wave morphology again suggesting a change in the location of the pacemaker cells either within the sinus node or to a site in close proximity to the sinus node (a wandering pacemaker), or a slight change in the heart's position with each inspiration and expiration.