Objective To observe the effect of Guanxinning Tablet (GXNT) on myocardial infarction and cardiac autonomic nervous function in rats with myocardial ischemia reperfusion injury (MI/RI). Methods Seventy SD rats were divided into 7 groups randomly (n=10); the sham group, the MI/RI group, 75 mg/kg, 150 mg/kg, 300 mg/kg and 600 mg/kg GXNT groups and 300 mg/kg Compound Danshen Tablets (DST) group. All rats were administered orally for 7 days, and then the MI/RI model was made by ligating the left anterior descending branch of coronary artery in rats. The changes of electrocardiogram were recorded and the electrocardiogram of J points and heart rate variability (HRV) parameters were analyzed. At the end of reperfusion, the myocardial infarct size was measured by using Evans blue and tetrazolium chloride (TTC) double staining, and pathological changes of myocardium were observed by HE staining. The changes of serum lactate dehydrogenase (LDH), creatine kinase (CK), malondialdehyde (MDA) and nitric oxide (NO) levels were also detected. Results Compared with MI/RI group, GXNT and DST groups were significantly reduced myocardial infarct size and inhibited the rising of serum LDH and CK activities (P< 0.05, P< 0.01), and also reduced the total or average value of J point during reperfusion (P< 0.05, P< 0.01). Meanwhile, GXNT and DST groups were markedly increased HRV and serum NO level as well as decreased serum MDA content (P< 0.05, P< 0.01), and improved myocardial tissue pathology. Conclusions GXNT can reduce the myocardial infarction in rats with MI/RI, and also improve the cardiac autonomic nervous function.