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: Valvular heart abnormalities have been reported in patients with Parkinson ' s disease ( PD ) treated with pergolide .
### Output Text:
Valvular heart abnormalities have been reported in patients with Parkinson ' s disease ( PD ) treated with <span class="chemical">pergolide</span> . 