Because of the characteristic clinical, morphological, and genetic diversity, HCM has held the curiosity of clinicians and researchers since its modern description almost 40 years ago. During this period, understanding of this complex disorder has increased dramatically. On the other hand, perhaps no other cardiovascular disease has presented similar challenges and controversy in terms of aetiology, diagnosis, natural history, and management. For practitioners not frequently engaged in the clinical management of patients with HCM, misconceptions may understandably arise and important questions invariably persist. Therefore, this seminar aims to summarise and place into thoughtful perspective many of these issues and to generate a profile of HCM that will be useful to the practising clinician.

Nomenclature, definition and prevalence HCM has been known by a confusing multitude of names, largely reflecting its heterogeneity, with many individual investigators characterising the disease on the basis of the most obvious clinical feature apparent in a particular cohort of patients. 1, 2 There has even been uncertainty as to whether HCM is best regarded as a single but diverse disease entity, or rather as a group of related and phenotypically similar disorders. HCM has become the preferred name because, unlike many other terms (eg, hypertrophic obstructive cardiomyopathy and idiopathic hypertrophic subaortic stenosis), it avoids the misleading implication that leftventricular outflow obstruction is an invariable component of the disease process. Also, HCM accurately describes this primary cardiac disorder in which the indispensable diagnostic characteristic is a thickened and non-dilated left ventricle (figure 1) in the absence of those associated conditions that could produce the magnitude of hypertrophy evident (ie, systemic hypertension, aortic valvular stenosis, and certain expressions of athlete’s