Since the symptoms can be very subtle, the only reliable method for detecting HCM, making an echocardiogram, or an autopsy in the event of death, is to perform an autopsy. Cats that have died of HCM usually have a relatively large heart with an enlarged left atrium. The diagnosis of HCM is made when other possibilities that can cause similar symptoms (such as increased thyroid function) are excluded. For several years, a DNA test is also possible at Maine Coons. To date, however, this offers an incomplete picture of whether or not HCM has developed. Cases are known of cats that turned out positive on the DNA test, but until old age does not show HCM when making the echocardiogram. The other way around also occurs: cats that come negative from the DNA test and still develop HCM. Not surprising when you consider that only one marker has been found in the Maine Coon, while in humans, a much larger number of these ‘abnormalities’ have been found.