Intensifies, with "up"
I believe the answer is:
heats
'intensifies with up' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for heats that I've seen before include "Makes hot or warm" , "Eliminating rounds in a contest" , "Haste (anag.)" , "Warms up for the preliminary races" , "Eliminating rounds of a race" .)