With its patent-pending design, Thundershirt"s gentle, constant pressure has a dramatic calming effect for most dogs if they are anxious, fearful or over-excited. Based on surveys completed by over two thousand customers, over 80% of dogs show significant improvement in symptoms when using Thundershirt. Thundershirt is already helping tens of thousands of dogs around the world, and is recommended by thousands of Veterinarians and dog trainers. XXS - CHEST SIZE 9"-13.5" 110 lbs.