Why is it dangerous to thow cold water over a heatstroke victim?

It is not recommended to throw cold water over a heatstroke victim because sudden cooling can constrict blood vessels and divert blood flow from vital organs to the skin, making heat dissipation more difficult and worsening the heatstroke. Instead, the recommended first aid for heatstroke involves gradually cooling the person by applying cool, wet cloths or spraying them with a hose and fanning them to promote evaporation.