From Longman Dictionary of Contemporary Englishheatstrokeheat‧stroke /ˈhiːtstrəʊk $ -stroʊk/ noun [uncountable] MIfever and weakness caused by being outside in the heat of the sun for too long → sunstroke
Examples from the Corpus
heatstroke• Guys would pass out from heatstroke.• As the victim's temperature rises higher and higher, they suffer internal heatstroke and all their organs gradually fail.• After a heroic week of earth moving, he went down with heatstroke. 