Heat stroke is a serious condition that is caused by your body overheating, typically from physical exertion in high temperatures, or prolonged exposure to high temperatures. Heat stroke is most common in the summer months, when the temperature gets hot. If left untreated, damage can be done to the kidneys, muscles, heart and brain, which can result in serious complications or even death. Heat stroke can be recognized as some of the following symptoms found after exposure to high temperatures. The main sign of heat stroke will be a core temperature of 104F(40C), or higher, obtained using a thermometer. Strange behavior can also be a sign of heat stroke, in the form of confusion, slurred speech, agitation, irritability, delirium and in severe cases seizures and coma. Feeling nauseous or vomiting is also a sign of heat stroke. Flushed skin, rapid breathing, a racing heart rate and headache are also signs of heat stroke.