Listen to the first thump or pulse (9)
I believe the answer is:
heartbeat
'pulse' is the definition.
(I know that pulse can be written as heartbeat)
'listen to the first thump' is the wordplay.
'listen to' becomes 'hear' (to hear something is to listen to it).
'the first' becomes 't' (1st letter of 'the').
'thump' becomes 'be at' (synonyms).
'hear'+'t'+'beat'='HEARTBEAT'
'or' is the link.
(Other definitions for heartbeat that I've seen before include "Circulation noise" , "Pulse of cardiac origin" , "Animating force" , "Essential pulsation" .)