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: The efficacy of denopamine , an orally active beta 1 - adrenoceptor agonist , in improving cardiac failure was assessed in dog heart - lung preparations .
### Output Text:
The efficacy of <span class="chemical">denopamine</span> , an orally active beta 1 - adrenoceptor agonist , in improving cardiac failure was assessed in dog heart - lung preparations . 