Duchenne cardiomyopathy is an inherited, X-linked neuromuscular disorder reported in dogs, particularly Golden Retrievers. A similar disease, called X-linked muscular dystrophy, has been reported in Irish Terriers, Samoyeds, and Rottweilers. These diseases may result in myocardial as well as neuromuscular disease. ECG abnormalities include deep and narrow Q waves, a shortened P-R interval, sinus arrest, and ventricular tachyarrhythmias. Echocardiography may demonstrate focal hyperechoic lesions affecting primarily the left ventricular and papillary muscle myocardium. The disease usually develops by 6–7 months of age, with the lesions decreasing in size throughout the next 2 years. The lesions result from calcification and fibrosis. In animals that survive, myocardial failure may develop.