Canine dilated cardiomyopathy (DCM) is a disease with high morbidity and mortality and with a high prevalence in certain breeds. Predominatly large breeds are affected, such as Great danes, Newfoundlands, Deerhounds and Dobermanns. One exception is Cocker spaniels, where both American and English Cocker spaniels are affected in a quite high frequency. Cardiomyopathy is characterised as a disease that affects the myocardium and gives an impaired heart function. To diagnose DCM following criteria have to be observed: 1. Dilation of the left ventricle. 2. Reduced systolic heart function. 3. Increased sphericity of the left ventricle. To be certain of the diagnosis, alternative reasons for the symptoms such as lung- and heart diseases with other etiologies have to be excluded Two different types of DCM have been found upon histological examination.