Friday could be the hottest day of the year so far, with Environment Canada predicting a high of 32 degrees for Toronto with the humidex expected to top out at 40.
The weather agency could declare a heat alert, which would mean pet owners in Mississauga have to be careful about where they leave their pets and for how long.
A new pet bylaw that went into effect Wednesday and among the changes, no pets can be left outdoors during extreme weather except for brief walks or exercise unless the pet has access to adequate shelter to protect the animal.
There are also new regulations on the size of pens that dogs can be held in, which are nearly three times the previous allowable size.
Dog houses must now be insulated, have clean dry bedding and shade and be large enough for the dog to stand up, turn around lie down and stretch out completely.