The mammalian heart
Chronic exercise results in increased pumping efficiency, a greater filling capacity and greater responsiveness of the heart to increased energy demands.
This diagram of the heart indicates the aorta, superior vena cava, right and left atria, pulmonary valve, tricuspid valve, inferior vena cava, left and right ventricle, aortic valve, mitral valve, pulmonary artery, and pulmonary vein.
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"Diagram of the human heart (cropped)."
http://commons.wikimedia.org/wiki/File:Diagram_of_the_human_heart_(cropped).svg
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