A dog's sudden heartbeat and shortness of breath may be caused by heart disease, respiratory disease, etc. It is best to go to the hospital for examination and treatment to avoid aggravation of the condition and delay in treatment. Generally, dogs will have a faster heartbeat and shortness of breath after exercise, when it is hot, and when they are excited. Therefore, if your dog has heart disease, it is best not to take the dog for strenuous exercise. In summer, when it is too hot, give the dog some exercise. Dogs take shelter from the heat to avoid dog heatstroke.