These ECG strips are from a 33 year old male and suggest a wandering atrial pacemaker. Note the slight change in P wave morphology that occurs as the P-P interval changes in a phasic fashion. This may represent a shift in pacemaker location within the sinus node itself or between the sinus node and an atrial ectopic focus that is located in close proximity to the sinus node. An additional possibility is that the minor P wave changes reflect slight changes in the heart’s position within the chest with inspiration and expiration.