Fibrosis is an important pathology of heart failure for the patients with coronary artery disease and dilated cardiomyopathy. The activation of renin-angiotensin-aldosterone system plays a key role during the progression of heart failure. Small dosage of spironolactone has been proven its effect on inceasing the survival of the heart-failure patients with the eject fraction lower than 35%. Meanwhile, a few studies found aldosterone levels of LV myocytes increased both in HCM patients and HCM transgenic mice. Furthermore, spironolactone, a mineralocorticoid receptor antagonist, could reserve interstitial fibrosis, attenuate myocyte disarray by 50%, and improve diastolic function in HCM transgenic mice.