Well... heat stroke is a loose term, but true heat stroke is when your core temperature exceeds 37.2 degree celsius to 39 for a period long enough for muscle meltdown to begin.
In effect, your body shuts down many of the heat generating muscular functions temporarily and you get true heat stroke, which can be life threatening.
What people normal refer to heat stroke is more along the lines of heat flash, where your core temperature is higher than normal but not critical temps for a sustained period of time coupled with dehydration.
For instance, if you left someone asleep locked in the back of a taxi in Goa for about 45 minutes with the window closed they might get heat stroke due to the rising temp and core temperature effect. However, if the window was open just a little bit, they might only get heat flash and recover within a few hours.
Remember this next time bastards