Aim To observe the mRNA expression of endothelial nitric oxide sythase (eNOS) at different time intervals after acute myocardial infarction in rat hearts and examine the effect of acute myocardial ischemic stimulation on the protein production of inducible nitric oxide sythase (iNOS) in rat hearts. Methods Forty-eight healthy Sprague-Dawley rats (200～250 g) were randomly divided into two groups: control group and ischemia group. Myocardial ischemia was induced by the left anterior descending coronary artery (LAD) ligation. Animals with LAD occlusion (ischemia group) were sacrificed at 1 h, 2 h, 8 h, and 24 h after operation. The eNOS gene expression in ischemic myocardium was assessed using reverse transcriptase-polymerase chain reaction (RT-PCR) standardized with β-actin; the iNOS protein in spare cardiomyocytes in the infarcted region after operational 8h was detected using immunohistochemedical analysis. Results Ligating of LAD for 2 h decreased significantly the eNOS mRNA levels in ischemic myocardial tissue compared with that in controls (p<0.05). The decent of eNOS mRNA level sustained for post-operational 24 h. There is no significant difference in expression level between ligating for 2 h group and ligating for 24 h group. iNOS protein was abundant in the 8 h infarcted heart in spared cardiomyocytes in the infarcted region. Staining of sham-operated rat hearts indicated the absence of iNOS protein. Significant difference in expression levels were observed between ischemia experiment groups and sham-operated control groups (p<0.01). Conclusion The eNOS gene expressed in normal rat hearts, whereas there was no iNOS protein expression in normal rat hearts. The expression of eNOS mRNA in ischemic myocardium after myocardial infarction in rats decreased in the early time. Acute myocardial infarction induced iNOS protein levels expressing abuntantly in the ischemic myocardium tissue in rats.