Dogs cool down very differently to us, mainly through panting and a little through their paws, which means heat can build up faster than owners expect, and more suddenly in flat-faced breeds, older dogs, or dogs carrying extra weight.
Cooling that helps, and cooling that makes it worse
Cool (not ice-cold) water poured or sponged over the neck, chest, belly, and paws is the fastest safe way to bring a dog's temperature down. Because ice or ice-cold water can make blood vessels close down near the skin, this actually traps heat in rather than releasing it. Move to shade, get air moving, and offer small sips of water rather than big gulps at once.
Signs to watch for
Step by step
Move into shade and pause the walk
Get off hot ground and out of direct sun as soon as possible. Be aware that hot pavement and tarmac can burn paws, while contributing to overheating the whole dog.
Cool with water, not ice
Pour or sponge cool water over the neck, chest, belly, and paws. Ice-cold water can close down blood vessels and slow cooling rather than speed it up.
Get air moving
A breeze, a fan, or a car's air conditioning all help evaporation do its work.
Offer small amounts of water
Encourage your dog to drink a little water, at small intervals, rather in large gulps (which could trigger vomiting and loss of further fluids).
Ring the vet and keep going
Cooling is first aid, not a cure. A dog that has overheated severely needs to be checked over carefully, even once it seems to be recovering.
Heatstroke can worsen quickly, and the outside temperature doesn't need to be extreme for it to happen. Keep alert to symptoms listed above, and take action quickly when you notice relevant symptoms.