Touch the heart of secret admirer (3)
I believe the answer is:
tad
'touch' is the definition.
(I've seen this before)
'the heart of secret admirer' is the wordplay.
'the heart of' indicates the answer is hidden within the clue.
'TAD' can be found hidden inside 'secret admirer'.
(Other definitions for tad that I've seen before include "Slight amount" , "A small amount (colloq.)" , "Small bit" , "(A) bit, touch" , "Modest amount" .)