Pulse in dicky heart always lagging initially (4)
I believe the answer is:
dhal
'pulse' is the definition.
(I know that Dhal is a type of pea)
'dicky heart always lagging initially' is the wordplay.
'initially' indicates taking the first letters.
The initial letters of 'dicky heart always lagging' is 'DHAL'.
'in' acts as a link.
(Other definitions for dhal that I've seen before include "Pakistani veg" , "Indian puree of pulses" , "Indian lentil dish" , "Pigeon-pea" , "Pigeon pea" .)