Why do you need your heart when you've already got lungs to pump oxygen throughout your body?

The heart is needed because it pumps oxygen-rich blood to all parts of the body, including the lungs. The lungs only exchange oxygen and carbon dioxide with the air, while the heart circulates the oxygenated blood to nourish the body's cells and remove waste products. Both the heart and lungs work together to ensure the body receives the oxygen it needs to function properly.