A cat’s purr vibrates between 25 and 150 hertz — a frequency range that has been shown to promote bone density and accelerate tissue healing. Cats purr not only when they are content, but also when they are injured or stressed. It is their own built-in healing mechanism. Some researchers believe that living with a purring cat may lower your risk of heart disease by up to 40%. A quiet, furry, vibrating companion — nature’s most gentle therapist.