Rise rapidly and so far heartlessly (4)
I believe the answer is:
soar
'rise rapidly' is the definition.
(synonyms)
'so far heartlessly' is the wordplay.
'far' becomes 'afar' (synonyms).
'heartlessly' suggests removing the centre.
'afar' with its middle removed is 'ar'.
'so'+'ar'='SOAR'
'and' acts as a link.
(Other definitions for soar that I've seen before include "Rise high in flight" , "rise dramatically" , "Increase rapidly" , "Ascend, fly upwards" , "Rise high into the air" .)