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: Improvement by denopamine ( TA - 064 ) of pentobarbital - induced cardiac failure in the dog heart - lung preparation .
### Output Text:
Improvement by <span class="chemical">denopamine</span> ( <span class="chemical">TA - 064</span> ) of <span class="chemical">pentobarbital</span> - induced cardiac failure in the dog heart - lung preparation . 