Answer:
The heart. One of the most important organs in our body which include the brain, the liver and many others which i myself dont know about.
The heart pumps blood to every organ in the body yes even your lips. Keeping the heart healthy is not a choice if you want to live.
The heart pumps pure/oxygenated blood to the body organs and once used , the impure/de-oxygenated blood is pumped back to the lung where carbon dioxide is taken out while oxygen is taken in by the blood. This process goes on and one without ever stopping (unless its the day you leave the world behind)
Not only the process above but also many others . Like helping the liver to clean the blood from impurities (thats the only other that i know)
Hope its helpful ☆