Beat regularly (5)
I believe the answer is:
throb
'beat' is the definition.
(throb is a kind of beat)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for throb that I've seen before include "Beat quickly from excitement etc" , "Sound of engines" , "Pulsate; regular beat" , "One's heart may do it" , "Beat strongly" .)