I don't know exactly but my Vixen has some turkish angora in her and none of my other cats are panters. She is big time. I was terrified as my friend had told me of her DSH that panted and they found out it was a heart murmer or a hole in the heart I can't remember which. She had scheduled a neuter for her boy when her boyfriend's mom suggested mentioning the panting. Red flags went up from the vet as it is not normal. He postponed the neutered and told her that they needed to run an EKG. It was en expensive test cost approximately $300.00 but this test found the heart defect. The vet suggested not doing the neuter as putting the cat under anistetic could be deadly. So actually this cat is on meds now as to keep him calm and not cause added stress that could cause him harm. When she told me about this I panicked as Vixen is an excessive panter. She was due to get spayed and there was no way I was having her put under anistetic without knowing if there was something wrong. The vet did the the EKG and ultrasound, blood work the whole nine yards all came back perfectly normal. He said some cats do this. It is rare and it sometimes comes from particual breeds. AS Vixen is not a pure breed anything he could only speculate that it was probably that she had one of these breeds in her genetic make up and that is why she does it. Not all turkish angora's do this but apparently there is a defective gene which causes it. And it can occur in any cat. He told me that the best thing to do was what I did and get her tested to make sure it was not a heart defect as 9 times out of 10 that is what it is.