Sphygmus; rhythm (5)
I believe the answer is:
pulse
This clue is a double definition.
'sphygmus' is the first definition.
(I've seen this in another clue)
'rhythm' is the second definition.
(I have seen 'Regular rhythm ' mean 'pulse' so perhaps 'rhythm' could also mean 'pulse')
(Other definitions for pulse that I've seen before include "Bean - throb" , "When you're gone, you haven't one" , "Vitality" , "enjoyed by vegans?" , "Heart rhythm" .)