It was due to take place yesterday, when temperatures peaked at 29 degrees Celsius.
Organiser Geoff Raynsford said: “We had to cancel our dog show because of the predicted high temperatures. This might have been dangerous for the dogs, so it was a hard decision to make, but it was the right one.
“Our Facebook page has been flooded with support, saying it was the right decision.”
Worthing Borough Council straightaway agreed the dog show could be held on Sunday, August 26, instead.
Findon Valley Fun Dog Show returns to The Gallops for its fifth year, with the aim to raise desperately-needed funds for Paws Animal Sanctuary and Sussex Pet Rescue.
Geoff Raynsford said: “We have been striving to provide owners and their beloved dogs with an afternoon of goodwill and fun.
“This year we will be able hosting a barbecue, tea, coffee and homemade cakes, a bouncy castle for the kids and stalls selling a selection of handmade products.
“Alongside the show ring, there will be a Hoopers agility ring, run by Sue Davies from Dog Tales and Sue Knowles, who owns a local canine hydrotherapy centre.
“All those involved are dog lovers. Last year, we were able to present the charities with donations for £500 and £1,100. The more we can give, the more sick and abandoned animals they can help.
“Please come along and help us on the day. Every pound you give will help an animal in need.”
Registration starts at midday and the first class will be at 1pm.
Dog wardens Pat Eaves and Russ Akehurst will be judging. There will be a rosette for the first six in each class and a bag of treats for the first three.
All of the children in the child handler class will receive a rosette.