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. It is this pressure that has a dramatic calming effect for most dogs if they are anxious, fearful or over-excited. From real world experience, we know with certainty that Thundershirt DOES WORK. That is why we are able to offer a money-back guarantee. Based on surveys completed by over 1,000 Thundershirt users, over 85% of dogs show significant improvement in anxiety symptoms when using Thundershirt.