I've known him, and am traumatized at the concept of maybe losing him to a heart problem. I know absolutely nothing, and I also don't know if maybe it's something with the breed. The devons are an unusual breed, and maybe you know something about them. If you know anything, i'd be very appreciative. I have not been able to find a list of congenital heart problems by cat breed but I will keep looking for something, because there are such lists for dogs.
Cats have heart murmurs for many reasons.
There is even a described disorder in cats in which there is a murmur that gets louder with exercise or excitement but for which no underlying heart disease can be identified. Unfortunately, this pattern of murmur is also recognized as occurring with cardiomyopathy in cats, which is the most common cause of heart murmurs and usually will lead to later problems. We have several cats in our practice who have had heart murmurs all their lives without any apparent problems from them and at least one of these cats is well into his teens. We see cats with hypertrophic cardiomyopathy who have problems by the time they are several months old. The only really good way to identify the cause of a heart murmur in cats is an ultrasound exam.