Aim To investigate whether the anti-fibrosis effect of spironolactone in heart is associated with the expression of silent information regulator 1 (SIRT1). Methods 40 male Sprague-Dawley rats were randomly assigned to 4 groups:control group, model group, low-dose spironolactone group, and high-dose spironolactone group. The latter 3 groups were injected subcutaneously with isoproterenol [5 mg/(kg·d) for 7 days] to establish rat myocardial fibrosis model. The rats of low-dose spironolactone group and high-dose spironolactone group were given 30 and 60 mg/(kg·d) spironolactone intragastric administration at the same time of injecting isoproterenol, while the control group was given the same volume of normal saline for 21 days. Changes of left cardiac function were detected by Powerlab physiological recorder, and pathological changes of myocardium were evaluated by HE staining and Masson staining. Western blot and real-time fluorescence quantitative PCR were used to detect the expression of SIRT1 in rat myocardium. Results The left ventricular weight index (LVWI), right ventricular weight index and left ventricular end-diastolic pressure (LVEDP) in the model group were significantly higher than those in the control group (P＜0.05). Left ventricular systolic pressure (LVSP), maximum change rate of left ventricular pressure rise (＋dp/dt_max) and maximum change rate of left ventricular pressure drop (－dp/dt_max) in model group were significantly lower than those in control group (P＜0.05). Compared with the control group, the myocardial arrangement was disorder, collagen fiber proliferation was obvious, and the expressions of SIRT1 mRNA and protein was down regulated in the model group rats (P＜0.05). After giving spironolactone, the levels of LVWI and LVEDP in rats were significantly lower than those in model group (P＜0.05), and LVSP, ＋dP/dt_max and －dp/dt_max were significantly higher than those in model group (P＜0.05). Compared with the model group, the degree of myocardial arrangement disorder decreased, the collagen content decreased, and the mRNA and protein expressions of SIRT1 increased in the spironolactone group (P＜0.05). Conclusion Spironolactone can alleviate myocardial fibrosis induced by isoproterenol in rats, and its anti-fibrosis effect may be related to the up-regulation of SIRT1 expression.