The aims of this study were to explore the changes in expression of myocardial adiponectin (APN), changes in serum APN, and the significance of bisoprolol intervention in acute myocardial infarction (AMI) rats. An AMI rat model was established for the purposes of this study and was used for analysis of serum APN as determined by ELISA. Changes in expression of myocardial APN mRNA and APN protein in AMI rats were determined via reverse transcriptase (RT)-PCR and immunohistochemistry. Serum APN concentration and APN protein expression of the myocardium decreased significantly in the AMI groups compared with the sham operation group, with the lowest serum APN and APN protein expression on day 7 after AMI. On days 7 and 10 after AMI, the expression of myocardial APN mRNA in the AMI groups decreased significantly compared with the sham operation group. However, the APN mRNA increased on day 10 compared with that on day 7. Notably, there was an increase in levels of serum APN and myocardial APN expression after bisoprolol intervention. The expression of myocardial APN and serum APN decreased in AMI rats. APN may be an important protective factor against AMI. Bisoprolol can also protect against AMI because it increases APN expression.