Older or circulatory dogs in particular are at risk on humid days. But basically any dog can suffer from heat stroke that is exposed to the sun or high temperatures without protection, for example inside a car.
Heat stroke is manifested by heavy panting, movement disorders, and staggering. A look at the gums shows the intensely bright red colored mucous membranes. In the advanced stage vomiting, shock and loss of consciousness occur.
The dog, especially its head, must be cooled immediately, preferably by showering with cold water. Massage the limbs to stimulate circulation. If there are signs of shock (rapid breathing, racing pulse, pale mucous membranes that only turn pink again after more than two seconds after pressure with the finger), the dog must be taken to the vet as soon as possible.
On humid (including cloudy) days, dogs should not take long walks or even bike rides, nor should they stay in the car. When staying outdoors, they must always have access to shaded areas and enough fresh drinking water.