The cardiomyopathies are an important, heterogeneous group of heart muscle diseases that make a significant contribution to morbidity and mortality.  They are associated with mechanical and/or electrical dysfunction. Inappropriate ventricular hypertrophy or dilatation is usually present.  Cardiomyopathy involvement may be predominantly limited to the heart (primary cardiomyopathy) or form part of a generalised systemic disorder (secondary cardiomyopathy). Causes vary widely, but genetic aetiologies are most common in primary cardiomyopathies. Complications include cardiovascular death and progressive heart failure, with its associated disability. 
In 1995, the World Health Organization/International Society and Federation of Cardiology Task Force classified cardiomyopathies as primary myocardial disorders, whereas heart muscle diseases of known aetiology or associated with systemic diseases were categorised as secondary or specific heart muscle diseases.  However, as research has improved the understanding of these conditions, working groups on both sides of the Atlantic have proposed new but different classification systems.
The European Society of Cardiology Working Group on Myocardial and Pericardial Diseases has opted to use a clinical rather than genetic classification, where heart muscle disorders are classified according to morphology and function: 'a myocardial disorder in which the heart muscle is structurally and functionally abnormal, in the absence of coronary artery disease, hypertension, valvular disease and congenital heart disease sufficient to cause the observed myocardial abnormality'.  Its members felt that many primary cardiomyopathies have significant extra-cardiac manifestations and that many secondary cardiomyopathies may involve the heart as the major manifestation.
The scientific statement from the American Heart Association has defined cardiomyopathies as 'a heterogeneous group of diseases of the myocardium associated with mechanical and/or electrical dysfunction that usually (but not invariably) exhibit inappropriate ventricular hypertrophy or dilatation and are due to a variety of causes that frequently are genetic. Cardiomyopathies either are confined to the heart or are part of generalised systemic disorders, often leading to cardiovascular death or progressive heart failure-related disability'. 
Primary cardiomyopathies are those where the condition is predominantly confined to the heart muscle and where subclassifications of genetic, mixed, and acquired are adopted.
Secondary cardiomyopathies are those where myocardial involvement occurs as part of a systemic or multi-organ disorder.
It is important to recognise that the traditional classification into hypertrophic, dilated, and restrictive cardiomyopathies mixes anatomical with functional designations, which are not mutually exclusive.
Director, Centre for Medical Education
School of Medicine, Dentistry & Biomedical Sciences
Queen's University Belfast
PM is an author of a reference cited in this monograph.
Royal Victoria Hospital
Belfast Health and Social Care Trust
AM has received speaker fees from Shire and Genzyme for speaking at educational meetings. AM is an author of a reference cited in this monograph.
Associate Professor of Medicine
Division of Cardiology
Johns Hopkins Medical Institutions
KW declares that she has no competing interests.
Guy's and St Thomas' Hospital
JC declares that he has no competing interests.
Manchester Royal Infirmary
VSM declares that he has no competing interests.
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