AIM To study the effects of nalox-one on plasma endothelin-1 and nitric oxide during myocardiac ischemia-reperfusion ( I/R ) injury. METHODS Using myocardiac ischemia models and myocardiac ischemia -reperfusion injury models that was made by means of ligating sinistra corona-ria arteria,to investigate the change of plasma ET-1 and NO during I/R injury, and after the protection and treatment with naloxone,an antagonist of opoid receptor. 40 New Zealand rabbits were randomly assigned to 4 groupsCischemia group, nalox-one protection group, naloxone treatment group and ischemia-reperfusion group, 10 in each group). The blood was phlebotomized at different time in each group. The concentration of ET-1 was detected with radioimmunology method and NO with nitrate reductase method. RESULTS The levels of ET-1 had the trend of improvement after ischemia and were at its peak at the end of 4 h, but the levels of NO were significantly decreased. The ET-1 levels were significantly improved after 0. 5-1 h of injury compared with that before ischemia (P < 0. 05) 5 whereas its levels were significantly low in naloxone protection group ( P < 0. 05 ) , but the treatment group showed no significant change except after 0. 5 h of ischemia(P>0. 05). The levels of NO decreased after injury , whereas its levels in naloxone protection group increased significantly compared with that before ischemia ( P 0.05). CONCLUSION Naloxone may effectively reduce the level of ET-1 and enhance the level of NO after myocardiac ischemia and during I/R injury; whereby it decreases the injury to vascular and myocardium.