Hypertrophic obstructive cardiomyopathy (HOCM) is the most frequently inherited cardiovascular disease (prevalence in the general population of 1/500) and is characterized by significant left ventricular hypertrophy, especially in the interventricular septum, combined with small-volume cardiac cavities. Transaortic surgical septal myectomy is the most commonly used technique to treat HOCM, and is associated with low operative morbidity and mortality and a reduction of the outflow gradients. The composite operative mortality of only 0.4% (17/3695 patients) from 5 major high-volume centers in North America highlights the role of dedicated HOCM units. The involvement of the mitral valve in the pathophysiology of HOCM has been addressed as systolic anterior motion (SAM)-related left ventricular outflow tract obstruction. Hypertrophic cardiomyopathy mitral malformations include leaflet elongation and a wide array of malformations of the papillary muscles and chordae that can be detected by transthoracic and transesophageal echocardiography and by cardiac magnetic resonance. Because they participate fundamentally in the predisposition to SAM, they have increasingly been repaired surgically.