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http://lsa.colorado.edu/essence/texts/lungs.html
https://www.innerbody.com/image_lymp01/card66.html
https://www.healthline.com/human-body-maps/portal-vein#2
https://boston.cbslocal.com/2017/01/30/bidmc-heart-health-2017-facts-about-cardiovascular/
https://www.khanacademy.org/science/health-and-medicine/circulatory-system-diseases
https://www.heart.org/en/health-topics/peripheral-artery-disease/about-peripheral-artery-disease-pad
https://medlineplus.gov/arrhythmia.html
https://www.healthline.com/health/congestive-heart-failure
https://www.circulationfoundation.org.uk/document-library/circulatory-system
https://www.healthline.com/health/circulatory-system-diseases#prevention
https://www.thoughtco.com/atria-of-the-heart-anatomy-373232
https://yourheartvalve.com/heart-basics/heart-valves/
https://www.webmd.com/heart/mitral-valve-prolapse-symptoms-causes-and-treatment
https://ctsurgerypatients.org/adult-heart-disease/tricuspid-valve-disease
https://www.livescience.com/39925-circulatory-system-facts-surprising.html