심장, 가슴, 마음,
I often find the words 심장, 가슴, 마음 and always be translated as "heart".
Can one replace each other?
Is there any difference in the meaning?
What kind of situation that makes them appropriate and not?

감사 함니다!

Question

심장, 가슴, 마음,
I often find the words 심장, 가슴, 마음 and always be translated as "heart". 
Can one replace each other? 
Is there any difference in the meaning? 
What kind of situation that makes them appropriate and not?

감사 함니다!

Answer

Sassafras already said it!
심장 is the term for the organ itself. Very literal and physical
가슴 actually means chest
마음 is more of a feeling/poetic/less literal/the idea of the heart

Answer

심장  usually means the organ in a physical way.
가슴 means chest, not the heart.
마음 usually describe the feeling in a physiological way.