In the early stages of HCM, there may be no clinical signs at all. A problem may only be suspected after
examination by a vet. Presence of a murmur or gallop rhythm may be noted on clinical exam, however is not present in all cases.
In the later stages of the disease, the most common clinical sign is a change in breathing – laboured or fast breathing. Changes may be subtle at first, but can become serious quickly, especially in stressed cats. Open mouth breathing is abnormal in cats, unlike panting commonly seen in dogs, and is a sign of extreme respiratory compromise.
Lethargy is seen in some cats, but may be difficult to appreciate due to the sedentary lifestyle of many cats. If a blood clot develops, your cat may suddenly become painful in, or lose the use of one or more limbs.
As many cats do not show any clinical signs until the very late stages of the disease, it is important to investigate any cat that is found to have a murmur or a gallop rhythm, even if they are symptomless.