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: Using both contaminated heparin products and the synthetically produced derivative , we showed that the OSCS produces dose - dependent hypotension in pigs .
### Output Text:
Using both contaminated <span class="chemical">heparin</span> products and the synthetically produced derivative , we showed that the OSCS produces dose - dependent hypotension in pigs . 