Heat syncope is fainting as a result of overheating (syncope is the medical term for fainting). It is another stage in the same process as heat stroke, it occurs under similar conditions, and it is not distinguished from the latter by some authorities. The basic symptom of heat syncope is a body temperature above 40°C (104°F) with fainting, with or without mental confusion, which does occur in heat stroke. Heat syncope is caused by mild overheating with inadequate water or salt. In young persons, it is far more common than true sunstroke.
Heat syncope occurs when blood pressure is lowered as the body dilates (widens) arterioles (small blood vessels) in the skin to radiate heat. Also, water is evaporated from the blood, reducing the blood's volume and therefore lowering blood pressure further. The result is less blood to the brain, causing light-headedness and fainting.
The basic treatment for heat syncope is like that for other types of fainting: the patient is positioned in a seating or supine position with legs raised. Water is administered slowly, and the patient is moved to a cooler area.