Betts J. G., Desaix P. , Johnson E. W., Johnson J. E., Korol O., Kruse D., Poe B., Wise J., Womble M. D., Young K. A.. Anatomy and Physiology. OpenStax. 2013. ISBN978-1-947172-04-3.
Betts, 2013, § 19.2 Cardiac Muscle and Electrical Activity Betts J. G., Desaix P. , Johnson E. W., Johnson J. E., Korol O., Kruse D., Poe B., Wise J., Womble M. D., Young K. A.. Anatomy and Physiology. OpenStax. 2013. ISBN978-1-947172-04-3.