Cardiomyopathy is a disorder of the heart muscle. There are two inherited forms in dogs: Dilated Cardiomyopathy (DCM) most frequently seen in Dobermans and Arrhythmogenic Ventricular Cardiomyopatny (ARVC) most associated with the Boxer. Cardiomyopathy is rare in Australian Shepherds. It is also important to note that the sudden catastrophic collapse sometimes caused by the cancer hemangiosarcoma, a common Aussie health issue, can be mistaken for cardiomyopathy. No Aussie should be presumed to have cardiomyopathy unless hemagiosarcoma has been ruled out.
Cardiomyopathies afflict older dogs, typically five years of age or more, though ages of onset and mode of inheritance vary between breeds with DCM. Dogs with DCM have enlarged (dilated) heart muscles; they will cough, have rapid heart rates, and shortness of breath. They sometimes die suddenly. The variations in disease onset and inheritance indicate that there are probably multiple forms of DCM.
In dogs with ARVC the heart muscle cells die and are placed with fat. The fat reduces the electrical conductivity of the heart, causing irregular heartbeats. Ultimately the heart will “short out” because the signals to beat can no longer reach a sufficient portion of the muscle and the dog dies. A dominant mutation with incomplete penetrance has been found for this form of cardiomyopathy in the Boxer.