Know the warning signs of heat-related illness and what to do if you or someone you know begins to exhibit them. Heat cramps—painful muscle spasms in the legs or abdomen—and heavy sweating may be the first signs of heat-related illness. Heat exhaustion is characterized by heavy sweating, weakness, clammy skin, fast or weak pulse, dizziness, nausea or vomiting, and fainting. Symptoms of heat stroke include throbbing headache, confusion, nausea, dizziness, shallow breathing, fainting, a body temperature above 103 degrees, and an altered mental state. For information about dealing with heat exposure, download a free Heat Wave Safety Checklist from the American Red Cross .