One of my biggest inspirations in animation in general is the work of Sylvain Chomet, and his dog in Belleview Rendez-vous is really fantastic - hugely fat with wee skinny legs that tremble under his weight!
For the scene with the man imagining cutting out the dog's heart I had a love heart pumping in the animatic. This confused a lot of people into thinking the dog was in love with the pancake woman. When I did the animation I found this diagram of a dog's heart and used this instead, which people seemed to find a lot clearer.
Muybridge's image sequences were really useful for scenes where the dog walks to and back from the kitchen, and the jumps off of and onto the bed.
The following is Plate 121 from Animals in Motion.