The one stirring heart in power (2,5)
I believe the answer is:
mr right
'the one' is the definition.
(both can mean the ideal partner)
'stirring heart in power' is the wordplay.
'heart' indicates the central letters.
'in' means one lot of letters goes inside another.
'power' becomes 'might' (synonyms).
The centre of 'stirring' is 'rr'.
'rr' inserted within 'might' is 'MR RIGHT'.
(Other definitions for mr right that I've seen before include "great match" , "Ideal future husband" , "Ideal union candidate" , "Perfect man (for someone)" , "Perfect husband" .)