Cardiomyopathy describes an abnormality of the heart muscle; hypertrophic refers to a thickening of the heart muscle. Causes of HCM include primary causes, such as genetics, and secondary causes, such as hyperthyroidism and hypertension. Primary HCM occurs more frequently in young male cats and in certain breeds, such as the Maine Coon. Secondary HCM tends to occur in older cats. Cats with HCM may not show overt signs in the initial stages of the condition. Cats with heart disease may have intermittent vomiting, changes in their breathing pattern, poor appetite, and behavior changes. Unfortunately, some cats receive the diagnosis after acute, unexpected death. Diagnosis of HCM is based on physical examination findings (e.g.: heart murmur or abnormal rhythm), chest x-rays, and ultimately with an ultrasound of the heart. As this insidious disease progresses, the heart muscle thickens and becomes stiff impeding blood flow through the heart. Heart failure may ensue if left untreated. A thickened, failing heart may cause blood to stagnate within the heart chambers and form clots. These blood clots shower to the body (thromboembolism) when the heart pumps; the clots often lodge in one of the back legs, leading to paralysis and pain. Treatment of HCM involves specific therapy for any secondary disease, treating arrhythmias, and therapy for heart failure if present.