In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: In isolated perfused heart preparations from isoproterenol - pretreated rats , the isoproterenol - induced maximal increase in left ventricular systolic pressure was significantly reduced , compared with saline - pretreated rats ( the EC50 of the isoproterenol - induced increase in left ventricular systolic pressure was enhanced approximately 22 - fold ) .
### Output Text:
In isolated perfused heart preparations from <span class="chemical">isoproterenol</span> - pretreated rats , the <span class="chemical">isoproterenol</span> - induced maximal increase in left ventricular systolic pressure was significantly reduced , compared with saline - pretreated rats ( the EC50 of the <span class="chemical">isoproterenol</span> - induced increase in left ventricular systolic pressure was enhanced approximately 22 - fold ) . 