Check concerning heartbeat (7)
I believe the answer is:
repulse
'check' is the definition.
(thesaurus)
'concerning heartbeat' is the wordplay.
'concerning' becomes 're'.
'heartbeat' becomes 'pulse' ('pulse' can be a synonym of 'heartbeat').
're'+'pulse'='REPULSE'
(Other definitions for repulse that I've seen before include "Repel" , "Rebuff, drive back" , "kick in the teeth" , "Send back" , "Beat off -- rebuff" .)