Background There are few studies to assess whether propofol attenuates myocardial ischemia-reperfusion injury via a mechanism related to nitric oxide (NO) route, so we designed this randomized blinded experiment to observe the changes of NO contents, nitric oxide synthase (NOS) activity, NOS contents in the myocardium, and cardiac function in ischemic reperfused isolated rat hearts, and to assess the relation between myocardial NO system and cardioprotection of propofol. Methods The hearts of 30 Sprague-Dawley male rats were removed, mounted on a Langendorff apparatus, and randomly assigned to one of three groups (n=10 each group) to be treated with the following treatments in a blinded manner: Group 1, control group, after perfusion with pure Krebs Henseleit bicarbonate (K-HBB) buffer solution for 15 minutes, hearts were subjected to 20 minutes global ischemia followed by 60 minutes reperfusion with pure K-HBB buffer; Group 2, after perfusion with K-HBB buffer solution containing propofol (10 mu g/ml) for 15 minutes, the hearts underwent 20 minutes global ischemia followed by 60 minutes reperfusion with the same K-HBB buffer solution; Group 3, after perfusion with K-HBB buffer solution containing propofol (10 mu g/ml) and L-NAME (100 mu mol/L) for 15 minutes, the hearts underwent 20 minutes global ischemia followed by 60 minutes reperfusion with the same K-HBB buffer solution. The cardiac function was continuously monitored throughout the experiment. The coronary flow was also measured. An ISO-NO electrode was placed into the right atrium close to the coronary sinus to continuously measure NO concentration in the coronary effluent. The tissue samples from apex of hearts in Groups 1 and 2 were obtained to measure the NOS activity by spectrophotometry and the NOS contents by immunohistochemistry, respectively. Results The cardiac function was significantly inhibited after ischemia and then gradually improved with reperfusion in all three groups. As compared with Group 1, the cardiac function variables and coronary flow at all the observed points were significantly improved in Group 2. The cardiac function variables and coronary flow were better in Group 3 than in Group 1, but were inferior in Group 3 than in Group 2. Both NO contents and NOS activity in the myocardium were significantly higher in Group 2 than in Group 1. However, NOS contents in the myocardium did not significantly differ between Groups 1 and 2. Conclusions In isolated rat hearts, propofol can improve cardiac functional recovery after ischemia-reperfusion by upregulating NOS activity in the myocardium. The NO system may play an important role in the preservation of myocardial ischemia-reperfusion injury produced by propofol. Chin Med J 2009;122(24):3048-3054