Heat-related emergencies occur when the body becomes dehydrated, which may result in an increased body temperature. Heat cramps, heat exhaustion, or heat stroke, can happen to anyone who stays in the summer heat and sun for too long.
Young children, the elderly, those with chronic illnesses such as heart disease, and those taking certain medications can become ill in hot, humid weather faster than healthy adults.
It is important for everyone enjoying the outdoors to know how to prevent heat emergencies, recognize when someone has been in the heat for too long, and be able to provide help when needed.
More information here from the Canadian Red Cross.