Other
Cartage: Normal Circulation
This thorough resource provides listing of ten unique characteristics peculiar to the cardiovascular system along with an examination of these ten factors individually.
Other
Cartage.org: Abnormal Circulation
Causes of heart failure, signs and characteristics of heart failure, pathologic conditions resulting in heart failure, and more are the topics addressed in this thorough resource.
University of Illinois
University of Illinois Urbana Champaign: The Heart of the Matter
A good quick look at the comparative anatomy of the heart of a typical bird and the human heart. Gives some of the facts behind the differences.