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: Vasopressin in the treatment of milrinone - induced hypotension in severe heart failure .
### Output Text:
<span class="chemical">Vasopressin</span> in the treatment of <span class="chemical">milrinone</span> - induced hypotension in severe heart failure . 