A survey about, at heart, God (6)
I believe the answer is:
apollo
'god' is the definition.
(Apollo is an example)
'a survey about at heart' is the wordplay.
'survey' becomes 'poll' (polling is a kind of surveying).
'at heart' means to look at the middle letters.
The middle of 'about' is 'o'.
'a'+'poll'+'o'='APOLLO'
(Other definitions for apollo that I've seen before include "Divine figure" , "Greek god (twin brother of Artemis)" , "Greek sungod, son of Zeus" , "London theatre" , "Greek god of light, poetry, music, healing and prophecy" .)