A comparative illustration of a normal heart and a heart affected by restrictive cardiomyopathy. Restrictive cardiomyopathy is a type of cardiomyopathy in which normal heart muscle is replaced by abnormal tissue, causing the ventricles of the heart become stiff and rigid. When the ventricles are unable to normally relax and fill with blood, the atria become enlarged and blood flow in the heart is reduced. Restrictive cardiomyopathy can be caused by diseases such as hemochromatosis, sarcoidosis, amyloidosis, or cancer treatments like radiation and chemotherapy.