The heart is a hollow, muscular, fish-shaped organ about the size of a closed fist. It's located approximately in the center of the chest. The average adult human heart weighs about 300 grams in men, and about 200 grams in women. About 50 million gallons of blood pass through the heart in an average lifetime. The heart beats about 70 times per minute at rest in adults, and from 90 to 140 times in infants.
Smaller hearts pump less blood with every beat than larger hearts.
As a result, smaller hearts need to increase their pumping capacity over time, a task they accomplish by beating faster. In addition to age and body complexion, physical and emotional state also affects the rate of heart beat. When a person is nervous or performs some kind of physical activity, the heartbeat speeds up. For example, if the heart beats 70 times per minute, we divide 60 second by 70. The heart is beating at an average rate of 72 beats per minute.