Put the vest on by threading it under the dog. Then overlap the velcro over the dog's back.
When this is done, it is important that the vest is not too tight at the back, there should be room for at least one cupped hand between the dog and the back of the vest.
If the vest is too tight at the back, the dog's movements are inhibited and the heat is not vented out of the vest as it should.
For more information, see the instructional video below.