Idiopathic dilated cardiomyopathy is a chronic heart muscle disorder of unknown etiology, but experimental and clinical evidence is accumulating that points to an immune pathogenesis in a subset of patients, and to the potential importance of myosin as an antigen. Most recent developments include evidence of cardiac- and disease-specific autoantibodies in a proportion of patients with dilated cardiomyopathy and their relatives, and the identification of immunogenic epitopes.