Abstract: AIM：To investigate the effect of chloride channel inhibitor, 4,4′-diisothiocyanostilbene-2,2′-disulfonic acid (DIDS) and free radical scavenger, edaravone (EDRV), on myocardial ischemia/reperfusion injury (I/RI) in vivo. METHODS: Male Sprague Dawley rats subjected to 30 min of myocardial ischemia and 4 h of reperfusion were divided into five groups: sham group, I/RI group, DIDS group, EDRV group and DIDS+EDRV group (eight rats/group). Rats were treated by program-controlled micropump injection of DIDS ［14 mg/kg, 4 ml/(kg·h), 2 h］ at the beginning of reperfusion, and EDRV (10 mg/kg) was injected into intraaortic sinus 5 min before reperfusion. Changes of left ventricle systolic pressures (LVSP) and the maximal first derivative of developed pressure (±dP/dtmax) were monitored from the time of myocardial ischemia to the end of reperfusion. Myocardial infarction size, serum creatine kinase (CK) activity, and lactate dehydrogenase (LDH) activity were determined at the end of reperfusion. RESULTS: Compared with those in I/RI groups, DIDS, EDRV or DIDS+EDRV treatment significantly reduced the size of myocardial infarction (n=8, P<0.05). LVSP and ±dP/dtmax were significantly improved in DIDS, EDRV or DIDS+EDRV treatment groups (n=8, P<0.05). Serum CK activity and LDH significantly decreased (n=8, P<0.05). No statistical difference was observed between DIDS and EDRV groups for the above-mentioned results. Compared with DIDS group alone or EDRV group alone, the combined administration of DIDS+EDRV had a stronger cardioprotective effect than DIDS or EDRV alone (n=8, P<0.05). CONCLUSION: No significant difference has been found in the protective effect of DIDS alone or EDRV alone on myocardial ischemia/reperfusion injury, but combined administration of DIDS and EDRV has a cumulative effect.