Cardiomyopathies are defined as cardiac diseases of the myocardium with associated cardiac dysfunction. They are cardiac diseases in which heart muscle disease and/or measurable deterioration of cardiac muscle function occurs due to various causes, such as genetic and sporadic mutations of muscle proteins, as well as external factors such as hypertension, ischemia, and inflammation. In 1995, the WHO/International Society and Federation of Cardiology (ISFC) classified primary cardiomyopathy caused by intrinsic factors into five groups according to the dominant pathophysiology: dilated cardiomyopathy (DCM), hypertrophic cardiomyopathy (HCM), restricted cardiomyopathy (RCM), arrhythmogenic right ventricular cardiomyopathy (ARVC), and unclassified cardiomyopathy. Among these cardiomyopathies, DCM is the most prevalent and the most common reason for cardiac transplantation in adults and children. Many recent findings indicate that genetic and sporadic mutations of a number of muscle proteins, such as myofibrillar, structural, and Ca²⁺ regulating proteins, can cause DCM. In such cases, certain mutations often induce DCM with cardiac arrhythmia that is recognized as a potential trigger of sudden cardiac death. Thus, effective prognostic determination and appropriate cardiac care depend on accurate molecular and genetic diagnoses.