Mammalian cardiovascular system.

Pulmonary (lung) circuit:

  1. The right ventricle pumps blood to the lungs

  2. via the pulmonary arteries.

  3. Blood in capillaries loads O2 and unloads CO2.

  4. Oxygenated blood returns via pulmonary veins

  5. to the left atrium and left ventricle.

Systemic circuit:

  1. Oxygenated blood leaves the heart via the aorta

  2. to capillaries in the head and arms, and also

  3. to capillaries in the abdominal organs and legs.

  4. Oxygen-poor blood returns via superior vena cava

  5. and inferior vena cava, then empty

  6. into the right atrium.