@inbook{1142556242, author={Kim E. Barrett and Susan M. Barman and Scott Boitano and Jane F. Reckelhoff}, title={Origin of the Heartbeat & the Electrical Activity of the Heart}, booktitle={Ganong's Medical Physiology Examination & Board Review}, publisher={McGraw-Hill Education}, address={New York, NY}, year={2017}, url={accessmedicine.mhmedical.com/content.aspx?aid=1142556242} }