<P> Heart muscle can also become damaged despite a normal blood supply . The heart muscle may become inflamed in a condition called myocarditis, most commonly caused by a viral infection but sometimes caused by the body's own immune system . Heart muscle can also be damaged by drugs such as alcohol, long standing high blood pressure or hypertension, or persistent abnormal heart racing . Specific diseases of heart muscle called cardiomyopathies can cause heart muscle to become abnormally thick (hypertrophic cardiomyopathy), abnormally large (dilated cardiomyopathy), or abnormally stiff (restrictive cardiomyopathy). Some of these conditions are caused by genetic mutations and can be inherited . </P> <P> Many of these conditions, if severe enough, can damage the heart so much that the pumping function of the heart is reduced . If the heart is no longer able to pump enough blood to meet the body's needs, this is described as heart failure . </P>

Cardiac muscles exhibit which of the following features