I noticed my cat, Unick, panting the first time during last summer. He goes with us over the moutains to eastern Wa. state. He travels well with just a harness and leash, and we were at the lake on a hot day. When he started hanging his mouth open I was worried at first. I knew that cats can't sweat and he was hot, so I just took him into the shallow water and sat him down. He was not at all opposed to the idea and he stood there in the water with me holding him for about twenty minutes. After that he was fine. He hates baths at home though. Last week he slipped his harness outside and was at large for 4 hours until after dark. My husband wasn't able to call him in. When I got home and got him in my spotlight, his mouth was hanging open and his toungue was out. Quite freaky looking, and he did it more after I got him in the house. I think he was very stressed this time, but he calmed down quickly. I think it is normal, but some cats do it more than others.