Primary restrictive cardiomyopathy is an extremely rare disorder of unknown cause. However, restrictive cardiomyopathy syndrome, a manifestation of amyloidosis, results from infiltration of amyloid into the intracellular spaces in the myocardium, endocardium, and subendocardium.

With both forms of restrictive cardiomyopathy, the myocardium becomes rigid, with poor distention during diastole, inhibiting complete ventricular filling. The myocardium also fails to contract completely during systole, resulting in low cardiac output.