Source: Zimmermann, Kim Ann. “Circulatory System: Facts, Function & Diseases.” Life Science, 16 Mar. 2018, www.livescience.com/22486-circulatory-system.html.
Source: “Exploring the Heart - The Circulatory System!” YouTube, AboutKidsHealth, 3 Feb. 2014, youtu.be/-s5iCoCaofc.
Source: “Heart and Circulatory System.” Edited by Yamini Durani, KidsHealth, The Nemours Foundation, Jan. 2013, kidshealth.org/en/teens/heart.html.
