Nobody has ever measured, even poets, how much a heart can hold.
Zelda Fitzgerald, 1900-1948, American Author and Wife of F. Scott Fitzgerald
I doubt it can be measured with any real accuracy. Perhaps we are born with an equal capacity, but living shrinks or swells every heart into a different shape and size. Their texture is altered also; some solid as stone, others flexible as elastic. Some are like butterflies or humming birds, alighting briefly or hovering nearby first this thing then that.
Some give away all they hold, while others only know how to take like greedy children. Hearts are true or false, hard or soft, each according to the nature of the being they are housed inside of. The correct answer depends on more than the size of the organ and the nature of the beast, but also upon what is kept there.
Does love take up more space than hate? Does bitterness cause more clutter than joy? Can laughter find a place beside jealousy or greed? Can a grudge crowd out grace? Will pain left unresolved become so swollen by constant tears that it fills all available space? Will a heart expand with one and shrink with the other, causing a lumpy confused surface? Do we take the time to clean when necessary, tossing out the debris that makes it beat with a rhythm so off-balance it keeps us lopsided? If not we certainly should; some mean and dirty things would be better off swept out, making space for things of greater value.
I do not believe there is an answer that would be universal, so we simply do not attempt to achieve one. But I do know that the heart is only limited in what it can hold by the reverence we have for the space it possesses. Fill it with negatives and it shrinks, wrinkles, then hardens. Fill it with positives and it will expand and overflow like a mighty fountain.
THINK ABOUT IT
LET IT GROW