The primary usage refers to someone who holds up under pressure,but the term is also used to mean someone who continues with a game well after it is obvious to everyone in the pool room that he has no chance
In this sense it can be applied to a fella that awaken to his bad game quits after losing only very few games
"Aw he has no heart"
It can be applied to the stakehorse who continues to play game after game in a losing sense
"now there is a good stakehorse,he has a lot of heart"
Often the person described puffs up with pride thinking ,that's right I gotta lot of heart"
Whereas the people paying the perceived compliment meant it more like this,"that poor fool
doesn't know when to quit,ie he is an idiot,if we ever get him down he'll never quit"
Heart is also more used in the lack of heart sense,let a man lose a game
regardless of the real reason,the idiots on the rail say"he got no heart"
usually this is just another way of saying ,Dean lost today.But the rift raft morons in the pool room
use the term like a dagger to pierce into the fellas reputation,the effect being the man who lost has no encouragement to ever play again.
Fear of being the laughing stock of the pool room exceeds his natural desire to win,so he becomes a railbird,a detective,a knocker
someone who does nothing but make pronouncements like"he got no hearyt"
soon the entire pool room is full of know it all critics,the action killers
the reason there is never much action