Record first heartless love letter (7)
I believe the answer is:
epistle
'letter' is the definition.
(I know that letter can be written as epistle)
'record first heartless love' is the wordplay.
'record' becomes 'EP' (abbreviation for extended play record).
'first' becomes 'ist' (ist resembles 1st).
'heartless' says to hollow out the word (remove centre letters).
'love' with its middle taken out is 'le'.
'ep'+'ist'+'le'='EPISTLE'
(Other definitions for epistle that I've seen before include "verse composition" , "one from Paul?" , "Letter from a saint" , "Biblical missive" , "a for instance" .)