To put some numbers to all of this:
Back in 2016, when most people didn't think twice about walking Fido during a heatwave, some researchers gathered information on 'heat related illness' (HRI; heatstroke) in dogs.
Out of a sample of 905,543 dogs, 395 cases of HRI in one year were taken to a vet. In other words, 0.04% of the dogs in the sample suffered HRI. That is one dog in 2500. Of those 395 cases, 56 dogs died: that is, one dog in about 16,000.
In another study, only just over half the cases of heatstroke with a known cause were the result of exercise (I assume the others were from being left in hot cars etc). That study had a slightly higher rate, but it was based on emergency vets who are likely to see more cases relative to the canine population as a whole. It also covered an exceptionally hot summer.
Both studies showed that brachycepahlic dogs were at considerably increased risk (about double). Chows were found to be at increased risk in both studies, along with some other breeds.
So... don't panic. Be sensible. Exercise caution - especially if your dog is brachycephalic, very young, very old, overweight, from a giant breed, has a very profuse coat, or is exceptionally active (springer spaniels seem to be at increased risk, but less so than pugs etc).
Both papers are available on the internet if anyone wants to read them. Plug in the titles, and they should come up.
- Incidence and risk factors for heat-related illness (heatstroke) in UK dogs under primary veterinary care in 2016, Hall et al, Scientific Reports, 2020
- Epidemiology of heat-related illness in dogs under UK emergency veterinary care in 2022, Beard et al, Veterinary Record, 2024