I don't think there is a verse that states pets go to heaven BUT my God loves me and knows heaven won't be heaven for me unless they are there. There would be no reason to allow certain animals in heaven and not others. I think they all go there. Animals were innocent victums of Adam and Eve's fall from grace. Because of them, animals were booted out of heaven because animals were under man's domain. When Jesus died and set mankind free; the animals were set free too. Animals are always in contact with their maker, He watches over every sparrow, after all.
There are horses in heaven. Jesus comes back on a white one. I take the Bible at it's word. It says horse. It means horse. There are other references about animals in heaven. Revelation 5:13 KJV is one.

NOTE: Beasts mentioned in the Bible no longer seem so odd to me since cloning has become a reality.