Flop as lover after heart transplant (5)

I believe the answer is:

loser

'flop' is the definition.
(I've seen this before)

I can't explain the remainder of the clue.

(Other definitions for loser that I've seen before include "Generally inept" , "One who frequently fails (colloq.)" , "One who is always a failure" , "Unsuccessful contestant" , "Roles for a non-winner" .)

I've seen this clue in The Times.

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