Aim To investigate the expression of poly ADP-ribose polymerase-1 （PARP-1） and to observe the effect of myocardial infarct size after the application of PARP-1 inhibitor 3-aminobenzamid （3-AB） in the early stage of my ocardial ischemia reperfusion （IR）in rat. Methods Rats （n＝164） were randomly divided into 6 groups: operation groups including operation 15 min, 30 min, 1 h, 2 h, 4 h, 6 h and 24 h group （12 rats in each group）, sham groups including sham 15 min, 30 min, 1 h, 2 h, 4 h, 6 h and 24 h group （6 rats in each group）, operation drug group （n＝14）, operation saline group （n＝12）, sham drug group （n＝6）, sham saline group （n＝6）. The left anterior descending coronary artery （LAD） was ligated for 45 min and reperfused for different time of 15 min, 30 min, 1 h, 2 h, 4 h, 6 h and 24 h, IR model was set up, then the rats were killed, and the expression of PARP-1 in myocardial tissue was detected. Sham group animals received all the surgical procedures described previously, but the LAD was not tied. Drug of PARP inhibitor 3-AB （20 mg/kg, iv） was given to operation drug group and sham drug group and the equal volume of saline was given to operation saline group and sham saline group at 30 min after thoracotomy and 45 min after reperfusion, then the expression of PARP-1 in myocardial tissue and the infarct size were detected. Results The levels of PARP-1 in operation groups were obviously higher than those in sham groups （P<0.05）. The level of PARP-1 in operation drug group was obviously lower than that in operation saline group （P<0.05）. Infarct size in operation drug group and in operation saline group after reperfusion 2 hour was obviously different （P<0.05）. Conclusions The content of PARP-1 gradually increased and dynamically changed in the early stage of myocardial ischemia reperfusion. Content of PARP-1 in myocardial after reperfusion for 2 hours had the most obvious expression. Drug of 3-AB obviously inhibited the level of PARP-1, decreased ischemia reperfusion injury and reduced infarct size. Actively using inhibitors of PARP-1 is significantly important in the early stage of myocardial ischemia reperfusion injury.