How the Cardiovascular System Works

The Heart and Oxygenation

 •   After delivering its supply of oxygen to your body, your less
     oxygenated (often called deoxygenated) blood circulates through
     your veins and returns to your heart through the right atrium. 

    From the right atrium, your blood passes through the tricuspid valve to
     your right ventricle. 

    The right ventricle pumps the deoxygenated blood through the
      pulmonary valve and into the pulmonary artery, which leads to your
      lungs. In your lungs, the blood’s hemoglobin binds oxygen, becoming “oxygenated.” 

    This oxygenated blood then returns from your lungs and enters your heart’s left atrium. 

    Because of pressure differences, oxygenated blood passes through the mitral (bicuspid) 
     valve into the left ventricle.

    The blood in the left ventricle is then pumped through your aortic valve and out your
     aorta, where it is distributed throughout your body via arteries and capillaries.

Blood’s Journey

Your blood travels at a very fast pace around your body, urgently trading its oxygen and other nutrients for carbon dioxide and wastes. The blood that returns to your heart contains fewer nutrients, more waste products, and is again less oxygenated.

Because deoxygenated blood is transported back to the heart via veins, it is also referred to as venous blood. Large veins have one-way valves, which help promote unidirectional blood flow back to the heart. 

Blood Returns to the Heart

Through your veins, your deoxygenated blood returns to your right atrium, just 20 seconds after it left your heart as oxygenated blood. It will repeat its passage through your heart thousands of times per day.