The World Health Organization restricts the use of the term “dilated cardiomyopathy” to diseases of unknown cause that primarily involve the myocardium. The term “idiopathic cardiomyopathy” would be more accurate to define a myocardial disease with no discernible cause using the current state of knowledge, while the term “dilated cardiomyopathy” refers to a cardiac remodeling process ultimately increasing the volume of the ventricular chambers with significant systolic dysfunction. The left ventricle is most frequently involved with usual extension to the right ventricle. Rarely is the right ventricle initially involved, as in right ventricular dysplasia. The presence of atrioventricular valve dysfunction is a common finding during the late stage of the disease. The mechanism of valve dysfunction is type IIIb with restricted leaflet motion of both anterior and posterior mitral leaflets caused by global ventricular enlargement ( Fig. 30-1 ). In most cases, the restricted leaflet motion and the associated annular dilatation are symmetrical, in contrast to ischemic mitral regurgitation. In the tricuspid position, severe tricuspid regurgitation originates from restricted leaflet motion involving predominantly the anterior and septal leaflets. Severe annular dilatation is always associated.

As defined, dilated cardiomyopathies form the largest group of heart diseases responsible for heart failure both in adults and in children. In the adult, the etiology in most patients is undetermined; however, knoweledge of its risk factors is important so that proper care of the patient can be undertaken ( Table 30-1 ). The familial form of the disease is present in 25% of patients. Genetic disorders are generally transmitted in an autosomal dominant manner.