See heart throb in chest then explode (5)
I believe the answer is:
burst
'explode' is the definition.
(I know that explode can be written as burst)
'see heart throb in chest' is the wordplay.
'see heart' says to take the centre.
'in' means one lot of letters goes inside another.
'chest' becomes 'bust' (bust can mean a woman's chest).
The middle of 'throb' is 'r'.
'r' going into 'bust' is 'BURST'.
'then' acts as a link.
(Other definitions for burst that I've seen before include "Crack" , "Explode, erupt" , "Suddenly break open" , "Explosion" , "Pop" .)