Figure 50-20 Diastolic dysfunction in hypertrophic cardiomyopathy (HCM). Increased chamber stiffness or decreased compliance occurs as a result of increased muscle mass and the resulting decreased ventricular volume. Increased muscle stiffness also occurs as a result of myocardial fibrosis. Thus, all three factors that affect the stiffness or compliance of the ventricle are altered in a way that increases chamber stiffness. Left ventricular relaxation in HCM is impaired because of changes in loading conditions, decreased inactivation, and increased nonuniformity. The subaortic stenosis in obstructive HCM represents a contraction load on the ventricle that delays and impairs relaxation. Coronary and ventricular filling loads, which aid in relaxation, are reduced in HCM because of the degree of hypertrophy and other reasons. High myoplasmic calcium results in decreased inactivation, which impairs relaxation both directly and indirectly by the relaxation process. Finally, much nonuniformity exists in HCM, another factor that also impairs relaxation. Thus, all three factors controlling relaxation are altered to impair it in HCM. (Redrawn from Wigle ED, et al: Hypertrophic cardiomyopathy. In Abelmann WH, Braunwald E [eds]: Cardiomyopathies, Myocarditis, and Pericardial Disease. Atlas of Heart Diseases, vol 2. Philadelphia, Current Medicine, 1995.)