There are 2 options: Original Kit (Sizes 0-5) *on Amazon* Expanded Kit (Sizes 0-8) After almost losing one of our puppies to flat chest, we created a cast to help treat the condition. Pectus Excavatum is an extremely dangerous condition in which a puppy is born with or develops a flat chest due to environmental factors. Luckily, there is a solution. Our kits come with several casts that your puppy can grow into, as needed. Depending on size and weight, the original kit will treat newborn - 4 week old puppies on average. There is an expanded kit available on our site as well. Please measure your puppy with our sizing chart prior to making a purchase! Its always important to consult with your veterinarian, as a flat chested puppy could have developed pneumonia or other respiratory issues through aspirations or other stress on the lungs. Please note, this kit has been designed around French Bulldogs, but has been successful in treating other breeds & even kittens. Feel free to reach out with any questions!