Your heart !
The flexor digitorum superficialis muscle in the forearm is roughly the size of your fist. It is responsible for flexing the fingers.
Size varies from person to person, but typically its about the size of its owners' clenched fist.
The muscles responsible for closing the fist are the flexor muscles located in the forearm. They include the flexor digitorum superficialis, flexor digitorum profundus, and flexor pollicis longus muscles. When these muscles contract, they pull on the tendons attached to the fingers and thumb, allowing the hand to make a fist.
The average size of the human heart is as big as your fist.
Your heart grows only through your teenage years, just like your bones, genitals and female breasts. The best way to understand the size of your heart is to compare it to the size of your clenched fist (punching fist). An infant's fist is much smaller than an adult's fist. The size of the heart is roughly equal to the size of the fist. The heart cannot continue growing through adulthood to old age because the cardiac muscle would not be able to fit in the chest or pump effectively if it kept growing. When the heart muscle is damaged and becomes flabby or unable to pump, the person can go into heart failure or can have a heart attack.
Your heart size can be measured by looking at your very own fist. For most people it is about the size of your fist.
The human heart is a pear-shaped structure about the size of a fist.
Your cardiac muscles is your heart. Make a fist with one of your hands. This is the closest and most accurate shape and size of YOUR heart.
The heart
like our fist ex: close your fist that is th size of our heart
Smooth Muscle