Main artery, part of that road going north (5)
I believe the answer is:
aorta
'main artery' is the definition.
(I've seen this before)
'part of that road going north' is the wordplay.
'part of' indicates the answer is hidden within the clue.
'going north' says the letters should be written in reverse.
'atroa' can be found hidden inside 'that road'.
'atroa' backwards is 'AORTA'.
(Other definitions for aorta that I've seen before include "Major artery of the body" , "Trunk route" , "Blood carrier" , "Vital blood vessel" , "Major artery at left of heart" .)