**1. Introduction**

The first officially accepted definition of cardiomyopathy was given by WHO in 1980 which defined it as "heart muscle diseases of unknown cause" to differentiate cardiomyopathy from cardiac dysfunction which occurs due to known cardiovascular diseases such as hypertension, coronary artery disease, or valvular disease [1]. WHO reclassified cardiomyopathies in 1995 to include diseases of myocardium associated with cardiac dysfunction that were earlier excluded. They expanded this criterion in order to include all known causes of cardiomyopathy and is based on anatomical and physiological features. It includes three main types of cardiomyopathy: hypertrophic (HCM), dilated (DCM), and restrictive (RCM).

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

In 2006, American Heart Association (AHA) in their document entitled "Contemporary Definition and Classification of the Cardiomyopathies" 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 dilation and are due to a variety of causes that frequently are genetic. Cardiomyopathies either are confined to the heart or are a part of generalised systemic disorders, often leading to cardiovascular death or progressive heart failure-related disability." According to the new AHA classification, cardiomyopathies are divided into two broad groups: primary cardiomyopathies and secondary cardiomyopathies. Primary cardiomyopathies encompass those that are exclusively or predominantly confined to the heart muscle and are acquired, genetic, or of mixed origin. Secondary cardiomyopathies include the subset of multiorgan involving diseases, which cause involvement of the heart as a part of their pathophysiology. In spite of this detailed classification, some confusion may arise because some primary cardiomyopathies may have associated extra cardiac components while as a few secondary cardiomyopathies can affect the heart exclusively.
