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: Peri - operative atrioventricular block as a result of chemotherapy with epirubicin and paclitaxel .
### Output Text:
Peri - operative atrioventricular block as a result of chemotherapy with <span class="chemical">epirubicin</span> and <span class="chemical">paclitaxel</span> . 