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: A restrictive pattern of valvular regurgitation , suggestive of the role of pergolide , was observed in 12 / 30 ( 40 % ) patients including two with heart failure .
### Output Text:
A restrictive pattern of valvular regurgitation , suggestive of the role of <span class="chemical">pergolide</span> , was observed in 12 / 30 ( 40 % ) patients including two with heart failure . 