Owners of flat-faced dogs are being warned to avoid over-exercising their pets during the hot weather.

French bulldogs, Boston terriers, pugs, and other brachycephalic breeds are particularly badly affected during hot weather.

They can struggle for breath and are more at risk of overheating, typically as a result of problems caused by extreme breeding.

Bulldog Blossom was left fighting for her life after her body temperature soared to 42°C during a warm day.

Owner Emma Darlington rushed her to Vets Now in Salisbury, Wiltshire, where she was kept in overnight.

Ms Darlington said: “Blossom was having a great time chasing a black Labrador and I think she just over-cooked herself. It was a warm day but it was by no means the heat of the midday sun.

“She was panting and gasping for breath. Then her tongue turned blue and started going darker and darker. It was an extremely scary situation to witness. I genuinely thought she had suffered a coronary.

Laura Playforth, veterinary standards director at Vets Now said: “There are two types of heat stroke — exertional and non-exertional.

“The first occurs during exercise and is much more common on hot sunny days, when dogs haven’t had a chance to acclimatise to the sudden rise in heat.

“The second type is when a dog is exposed to a notable rise in temperature but doesn’t have access to the ventilation, or drinking water, they need to keep themselves cool. This typically occurs in a parked car, a garden with no shade, or a very hot room.

“All dogs can overheat if left without water and outside for too long, so on hot summer days it's best to walk your dog in the morning or evening when it's cooler.

“And ensure drinking water and a cool, shaded spot is always available. It’s a good idea to clip hair if you have a longer-haired breed, and spray your dog with cool water as much as possible. Remember to never leave your dog in a hot car or a warm room.”

Heatstroke in dogs

It only takes a 2°C body temperature increase for heat stroke to kick in.

The illness occurs when dogs are no longer able to self-regulate and keep their temperature down, according to Vets Now, the UK’s leading provider of pet emergency veterinary care.

The most obvious sign of heatstroke in dogs is excessive panting and drooling. Other signs include overly red or purple gums; a rapid pulse; lack of coordination; reluctance or inability to rise after collapsing; seizures; vomiting or diarrhoea and in extreme circumstances, coma or death.