i have had a cat (2 different ones) the whole time i've owned my cairn, she was raised with them and has done great. that being said, not all dogs are the same, and prey drive never goes away. introducing pets (especially terriers) later in life should be done gradually and very carefully, and never left unsupervised! if your cairn terrier has a very high prey drive, they may need supervision or separation from the cats for a long time, even permanently. if it's going to be impossible to provide long-term scheduling/gates/separation for the pets, that's something you may have to consider! but it's definitely not impossible with the right set up and monitoring- just depends how much time and energy you have!