747/777/A340 and many others have 2 Holds sub divided into 5 Compartments. Forward holds have no heating so minus temperatures in flight. Compartments 3, 4 and 5 comprise of Hold 2 and adjoin. However, compartment 5 is heated for the transport of pets and livestock. Usually this is the tapered area at the a/c rear. The bins / containers will normally form a barrier to retain heat within that compartment. On opening the rear hold doors the area is often comfortably warm long after the cargo has gone.
I have no doubt our engineering contributers can furnish tech info and prescise temps.