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: Thus , consistent with its direct effect on heart , PAF appears to be implicated in bupivacaine - induced cardiovascular alterations .
### Output Text:
Thus , consistent with its direct effect on heart , PAF appears to be implicated in <span class="chemical">bupivacaine</span> - induced cardiovascular alterations . 