Objective: To observe the in vivo effect of Danlou Tablet (DLT) on myocardial ischemia and reperfusion (I/R) injury. Methods: DLT effects were evaluated in mouse heart preparation using 30-min coronary occlusion followed by 24-h reperfusion and compared among sham group (n=6), I/R group (n=8), IPC group (ischemia preconditioning, n=6) and DLT group (I/R with DLT pretreatment for 3 days, 750 mg.kg(-1).day(-1), n=8). The effects of DLT were characterized in infarction size (IS) compared with risk region (RR) and left ventricle using the Evans blue/triphenyltetrazolium chloride double dye staining method in vivo. Furthermore, the dose-dependent effect of DLT on I/R injury was evaluated by double staining method. Five different concentrations of DLT (0.625, 1.25, 2.5, 5 and 10 g.kg(-1).day(-1)) were chosen in this study, and dose-response curve of DLT was obtained on these data. Results: The ratio of IS to left ventricle was significantly smaller in the DLT and IPC groups than the I/R group (P<0.05 or P<0.01), the ratio of IS to RR was also reduced in the DLT and IPC groups (P<0.01), while there were no differences in RR among the four groups (P>0.05). Experiments showed incidence of arrhythmias was reduced in the DLT group (P<0.01). Furthermore, DLT produced a dose-dependent inhibitory effect with a half maximal inhibitory concentration of 1.225 g.kg(-l).day(-1). Conclusions: Our research concluded that DLT was effective in reducing UR injury in mice, and provided experimental supports for the clinical use of DLT.