Restrictive cardiomyopathy is the opposite of hypertrophic cardiomyopathy – it occurs when the heart muscle becomes elasticity (Eldredge, et. al., 2008). The heart is thus unable to relax and fill with blood normally, which causes elevated pressures. Pumping capacity and efficiency is decreased. In this disease, the heart walls are not thickened as in hypertrophic cardiomyopathy – “cats with this condition tend to have a very distended left atrium and are at a high risk of developing blood clots and congestive heart failure” (Eldredge, et. al., 2008, p. 321). Unfortunately, the prognosis is poor in the majority of cases, even with appropriate therapy. The causes of restrictive cardiomyopathy and other forms of unclassified cardiomyopathy are unknown; these diseases are nearly exclusive to cats.