For over four decades, the scientific community has struggled to characterise and understand the nature of the disease, or group of diseases, known as hypertrophic cardiomyopathy (HCM). A cursory look at the change in nomenclature over time (“acquired subaortic stenosis, in-stent stenosis, hypertrophic obstructive cardiomyopathy”, etc) suggests a constant development in the understanding of the disorder, as each generation of researchers isolates a novel feature that contradicts previously held dogma. Clarification of the underlying genetic background and the prognostic implications of the disease have been advanced by intense study of referral centre populations, but features of the pathophysiology of HCM can still surprise us, and novel findings, based on meticulous clinical observation, are still to be made. Two recent papers substantially alter our understanding of an important characteristic of HCM—namely, the prevalence of left ventricular outflow tract obstruction (LVOTO), and raise further questions as to the prognostic importance of such obstruction.

LVOTO was initially thought to be a fixed entity, defined by geometric abnormalities created by the asymmetric growth in the interventricular septum.1 Gradually, the refinement of two-dimensional echocardiography clarified the role of systolic anterior motion (SAM) of the mitral valve into the …