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: CONCLUSIONS : Verapamil promotes AF in normal dogs by promoting multiple circuit reentry , an effect dependent on intact autonomic tone and not shared by diltiazem .
### Output Text:
CONCLUSIONS : <span class="chemical">Verapamil</span> promotes AF in normal dogs by promoting multiple circuit reentry , an effect dependent on intact autonomic tone and not shared by <span class="chemical">diltiazem</span> . 