Aim To investigate the change in neuropeptide Y(NPY) Y1 receptor level in infarcted myocardium tissues of (MI) rats. 　Method MI was induced by ligating the left descending anterior coronary artery (LAD) in the heart of rats. The techniques of reverse transcription polymerase chain reaction (RT-PCR) were used to identify the exist of NPY Y1 receptor mRNA in myocardial tissues. The technique of semi-quantitative PCR wa s used to observe the change of NPY Y1 receptor mRNA level. 　Results NPY Y1 receptor mRNA distributed in the heart tissues of rat. Compared with sham operated rats ,the NPY Y1 receptor mRNA level both in infarction area and non-infarction area was increased significantly after MI fo r 1d and 3d. The NPY Y1 receptor mRNA level in the heart tissues of sham-op erated rats was also significantly increased compared with that in control rats . 　Conclusion These results suggest that MI may result in increase NPY Y1 receptor level in the heart tissues of rats. Stre ss stimulation such as surgery may also increase the NPY Y1 receptor level in the heart.