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: Mitral annuloplasty as a ventricular restoration method for the failing left ventricle : a pilot study .
### Output Text:
Mitral annuloplasty as a ventricular restoration method for the failing left ventricle : a pilot study . 