With its patent-pending design, Thundershirts 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 2000 customers, over 80 percent of dogs show significant improvement in symptoms when using Thundershirt. Pressure has a calming effect of the nervous system. Using pressure to relieve anxiety has been a common practice for years. Thundershirt is an excellent treatment for most types of dog anxiety and fear issues. It is also a very useful tool for managing excitability or hyperactivity with strangers, on the leash, or in a training environment. Thundershirts calming effects helps a dog to focus or refocus her energies in a more constructive direction, allowing training to be more effective. MD fits dogs with a 18 inch to 26 inch chest and that weighs 20 to 50 pounds.