Training in the heat

Hope you guys can offer some advice to my training problem.
I am currently stationed in Iraq courtesy of HM Forces. I have a turbo, HRM and cycle computer which gives speed and cadence. Problem is because of heat build up my pulse rises from 140 up to 165 by the end of a 45minute steady state lactate tolerance ride, keeping the same speed and cadence. (Max HR 180 bpm)
Would you suggest ignoring my rising HR and keeping speed the same during this session or easing off intensity to keep observed HR within set limits ??
Your advice / guidence would be appreciated Thanks