【Abstract】 Objective Using isolated rat heart ischemia reperfusion model to compare the effects on cardiac function and myocardial injury of giving Dobutamine at different time points after reperfusion and to explore the best time to use Dobutamine after myocardium ischemia reperfusion. Methods 36 male SD rats, establishing isolated heart ischemia reperfusion injury model in Langendorff perfusion apparatus with 15min equilibrium, 30min global ischemia and followed by 60min reperfusion., were divided into four groups (n=9) according to the method of completely random design. Different treatment was taken in reperfusion period. Ischemia reperfusion group (I/R group): reperfused with K-H solution; Dobutamine group one (Group D1): giving dobutamine infusion for 30min after 5min of reperfusion，other time perfused with K-H solution. Dobutamine group two (Group D2): giving dobutamine infusion for 30min after 15min of reperfusion，other time perfused with K-H solution. Dobutamine group three (Group D3): giving dobutamine infusion for 30min after 25min of reperfusion，other time perfused with K-H solution. Dobutamine infusion dose was 10ug/kg/min. Record heart function indexes of each group at the end of balance reperfusion (T0) and 10min (T1), 20min (T2), 30min (T3), 60min (T4) of reperfusion: heart rate (HR), left ventricular end diastolic pressure (LVEDP), left ventricular developed pressure (LVDP), the maximum rate of left ventricular pressure change (±dp/dtmax) and coronary flow (CF). Take the coronary flow at T0-T4 time points to measure the activity of LDH and CK according to the test methods attached to lactate dehydrogenase (LDH) and creatine kinase (CK) test kit. Myocardial infarct size (MIS) were measured with TTC staining method. SERCA2a and RyR2 expression was determined by Western bloting. Results After given dobutamine, HR, LVEDP, LDH and CK activity and MIS of Group D1 were higher compared with Group IR（P<0.05）. Meanwhile after given dobutamin, HR , CF, LVDP, ±dp/dtmax of Group D2 and D3 were higher than that of Group IR, but there was no significant difference in LVEDP, LDH and CK activity and MIS compared with Group IR (P > 0.05). SERCA2a expression between groups was no significant difference. While RyR2 expression were higher of groups with dobutamin compared with Group IR. There was no significant difference in data above between Group D2 and D3 after given dobutamine. Conclusion Giving Dobutamine after 15min of myocardial ischemia reperfusion in rats is superior to the other time points. Giving Dobutamine at this time point can timely and effectively improve the heart rate, increase the coronary flow, improve the myocardial contractile function, and does not aggravate the myocardial injury.