Dogs pant to show thirst, excitement, pain, fear or a reaction to heat. Panting is normal for dogs in all of these situations, but heavy, continuous panting may be a sign of heat exhaustion, illness or dehydration.
Primarily, pet owners see panting when their pet is excited and playful. Dogs are also prone to pant during lightning storms from a normal fear response.
When temperatures are high, dogs become hot and pant to draw cool air to circulate through their bodies. High levels of activity on hot days can lead to heatstroke. A veterinarian can determine if excessive or abnormal panting warrants medical attention.