It comes from the heart (6)
I believe the answer is:
artery
'it comes from the heart' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for artery that I've seen before include "main line" , "Principle channel of circulatory system" , "Blood vessel such as the aorta" , "Something that could be clogged" , "M1?" .)