Heat Stroke Occurs When Heat Production or Input Exceeds Heat Output, so Body Temperature Rises to Dangerous Levels

In hot, humid weather it is difficult for animals to lose heat because evaporative cooling cannot occur effectively. Strenuous exercise under these conditions can lead to a dangerous increase in body temperature. Similarly, when dogs are closed in cars in the sun, their panting saturates the air with water vapor, so further heat loss is impossible. As the body temperature rises, the metabolic rate increases, and more heat is produced. In addition, panting or sweating (or both) leads to dehydration and circulatory collapse, so it is more difficult to transfer heat to the skin. Once the body temperature exceeds 41.5^o to 42.5^o C (~107^o-109^o F), cellular function is seriously impaired and consciousness is lost.