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: After sacrifice the hearts of doxorubicin - treated animals were enlarged and the atria were hypertrophic .
### Output Text:
After sacrifice the hearts of <span class="chemical">doxorubicin</span> - treated animals were enlarged and the atria were hypertrophic . 