The Heart

The Heart:
The heart is a tough, hollow muscle about the size of a fist that pumps blood. The heart is enclosed in a tough sack of tissue called the pericardium. The average human heart beats about 70 times a minute, and with each beat it pumps about 5 ounces of blood, or about 4,000 gallons of blood each day. The heart rests in between beats, so it works less than half the time and rests more than half the time. In a 70 year lifetime, the average human heart works for about 30 years and rests for about 40 years.
The heart is not shaped like a valentine heart. Instead, it is pear-shaped.…