If your heart isn’t in it, there’s something very wrong (5)
I believe the answer is:
chest
'wrong' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for chest that I've seen before include "Large box; thorax" , "Box or trunk" , "Treasure box?" , "Trunk or crate" , "Rib area" .)