The first classification on this topic categorized cardiomyopathies as heart muscle diseases with dilated (DCM), hypertrophic, restrictive, arrhythmogenic right ventricular (ARVC), or nonclassifiable cardiomyopathy in 1980. 5 Subsequently, the World Health Organization/International Society and Federation of Cardiology classification in 1996 added inflammatory and viral cardiomyopathies as new and distinct entities. 5 With the development of molecular genetics, new classification schemes based on genomics such as the classification proposed by the AHA ensued, 6 which divided cardiomyopathies into 2 major groups based on predominant organ involvement. Primary cardiomyopathies (ie, genetic, nongenetic, and acquired) were defined as those solely or predominantly confined to heart muscle. Secondary cardiomyopathies had myocardial involvement as part of a large number and variety of generalized systemic (multiorgan) disorders, including systemic diseases such as amyloidosis, hemochromatosis, sarcoidosis, autoimmune/collagen vascular diseases, toxins, cancer therapy, and endocrine disorders such as diabetes mellitus. 6 The European Society of Cardiology (ESC) Working Group on Myocardial and Pericardial Diseases took a different approach based on a clinically oriented classification in which heart muscle disorders were grouped into specific morphological and functional phenotypes, including hypertrophic cardiomyopathies, DCM, ARVC, restrictive cardiomyopathies, and unclassified cardiomyopathies. Each phenotype was then subclassified into familial and nonfamilial forms. 7 Most recently, the MOGE (S) nosology system was developed, which incorporates the morphofunctional phenotype (M), organ (s) involvement (O), genetic inheritance pattern (G), etiologic annotation (E) including genetic defect or underlying disease/substrate, and the functional status (S) of the disease using both the ACC/AHA HF stages and New York Heart Association (NYHA) functional class. This nomenclature is endorsed by the World Heart Federation, is supported by an Internet-assisted application, and assists in the description of cardiomyopathy in symptomatic or asymptomatic patients and family members in the context of genetic testing. 8, 9

Classifications of cardiomyopathies that mix anatomic designations (ie, hypertrophic and dilated) with functional ones (ie, restrictive) can be quite challenging and have failed to satisfy the purposes of all users. 1 Confusion can arise because the same disease could appear in 2 categories (ie, hypertrophic and restrictive); there could be heterogeneity of clinical expression in different phenotypes, and some diseases do not have a uniformly static expression but evolve as a consequence of remodeling from one category to another during their natural clinical course (eg, hypertrophic cardiomyopathy, amyloid, and other infiltrative conditions can progress from a nondi-