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: Pergolide was discontinued in 10 patients with valvular heart disease , resulting in a lower regurgitation grade ( p = 0 . 01 ) at the second transthoracic echocardiography and the two patients with heart failure returned to nearly normal clinical examination .
### Output Text:
<span class="chemical">Pergolide</span> was discontinued in 10 patients with valvular heart disease , resulting in a lower regurgitation grade ( p = 0 . 01 ) at the second transthoracic echocardiography and the two patients with heart failure returned to nearly normal clinical examination . 