About the heart
The heart is the hardest working muscle in the human body. Located almost in the center of the chest, the adult human heart is about the size of a fist.
At an average rate of 80 times a minute, the heart beats about 115,000 times in one day or about 42 million times in a year. In a 70-year lifetime, an average human heart will beat more than 2.5 billion times. Even when a person is at rest, the heart continuously works hard.