The heart is the only organ in the human body that never rests. It continuously pumps blood throughout the body, providing oxygen and nutrients to every cell. This constant work is vital for life, as the heart stops beating, the body dies.
The brain is often thought to never rest as well, but this is not entirely accurate. While the brain is constantly active, it does have periods of decreased activity during sleep. However, even during sleep, the brain continues to perform essential functions such as regulating breathing, heart rate, and body temperature.
Some other organs, like the lungs and liver, also work tirelessly, but they do experience periods of reduced activity. For example, lung function decreases during sleep, and the liver regenerates itself during the night.
