Subendocardial sclerosis is a rare disorder of the cardiovascular system that affects both infants and children. Its characteristic feature is a thickening within the cardiac muscle lining of the atria and ventricles due to the increase in the quantity of inelastic collagen and elastic fibers.
The human heart has four chambers. These are the atria which act as holding chambers for blood, and the ventricles which pump blood out of the heart. Both of these chambers are separated by a partition called a septum. Valves connect the atria to the ventricles.
Subendocardial sclerosis is marked by diffuse endocardial thickening and myocardial dysfunction. Endocardial thickening is supposed to be caused by constant and heightened wall tension in the ventricles, perhaps secondary to damaged myocardium, mitral regurgitation, or both. This, however, changes with age progression. The disease may occur for no apparent reason (sporadic).