Circadian rhythms in human heart homograft

The electrocardiogram and cardiotachogram of a patient with a human heart transplant has been recorded for 72 hours. Within the donor P-QRS-T complex, one can identify the P waves emanating from residual sinoatrial heart tissue of the recipient. The recipient P waves are independent of the donor complexes. A clear circadian rhythm (23.4 hours) in heart rate is maintained for both donor and recipient tissue, the donor complexes preceding by a phase shift of 135 minutes the complexes of the recipient heart tissue. Both tissues display clear morning and evening minimum and maximum rates paralleling activity and lighting cycles.