this is one of the zero level comparison given to kids to understand the approximate size of human heart.
The size of the heart is 'somewhat' equal to that of a clenched fist in case of an average adult. There is no connection between the sizes of the two.
there is no biological mechanism , which can relate the size of the two .
AND ALSO , there is not any organ in our body whoose size we can compare as that of the heart ,
HOPE IT CLEARS YOU
ALL THE BEST ..