Bibliography
1. "Cactus Picture" <gnuhaus.com/iblog/ cactus_heart_big.jpg> March 16, 2005.
2. Campbell, Neil A. (2002) "Biology" 6th edition. Benjamin Cummings. San Francisco, CA.
3. Kay, Ian. (1998) "Introduction to Animal Physiology" Springer-Verlag New York Inc.
4. McWilliam, J.A. (1888) "On the Rhythm of the Mammalian Heart" Froceedings of the Royal Society of London, Vol. 44, pages 206-208.
5. NOVA. " Cut to the Heart” PBS Online <http://www.pbs.org/wgbh/nova/heart/> 1997.
6. Pool, Robert. (1990) “Heart Like a Wheel” Science, Vol. 247, No. 4948, pages 1294-1295.
7. Putnam, Jeremiah L. "Heart Diagram" Professor of Biology. Davidson College.
8. Schmidt-Nielsen, Knut. (1997) "Animal Physiology: Adaptation and environment" Fifth Edition. Cambridge University Press. New York, NY.