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: It is concluded that bepridil reduces heart rate by acting directly on the sinus node .
### Output Text:
It is concluded that <span class="chemical">bepridil</span> reduces heart rate by acting directly on the sinus node . 