A second example of an electrocardiogram following heart transplantation is shown here. It is from a 26 year old female following successful heart transplantation. The P waves labeled P1 are from the donor heart. Their rate is 113 beats/min (P-P interval = 0.53 sec) and they conduct to the ventricles with a PR interval of 0.12 sec. The P waves labeled P2 are from the atrial remnant of the patient’s original heart. Their rate is 125 beats/min (P-P = 0.48 sec) and they do not conduct to the ventricles.