Urges individual to measure initial heartbeats (8)
I believe the answer is:
impulses
'urges' is the definition.
('impulse' can be a synonym of 'urge')
'individual to measure initial heartbeats' is the wordplay.
'individual' becomes 'i' (Roman numeral for one).
'to' is a charade indicator (letters next to each other).
'initial' suggests taking the first letters.
'heartbeats' becomes 'pulses' ('pulse' can be a synonym of 'heartbeat').
The first letter of 'measure' is 'm'.
'i'+'m'+'pulses'='IMPULSES'
(Other definitions for impulses that I've seen before include "Sudden urges or stimuli" , "Sudden inclinations to act" .)