Beat seed (5)
I believe the answer is:
pulse
I believe this clue is a double definition.
'beat' is the first definition.
(I know that pulse is a more specific form of the action beat)
'seed' is the second definition.
(I've seen this before)
(Other definitions for pulse that I've seen before include "Rhythmical throb of arteries" , "Healthy food" , "Musical beat; edible seeds" , "Throb, beans" , "runner, possibly" .)