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: Diltiazem did not affect ERP , AF cycle length or AF duration , but produced conduction acceleration similar to that caused by verapamil ( n = 5 ) .
### Output Text:
<span class="chemical">Diltiazem</span> did not affect ERP , AF cycle length or AF duration , but produced conduction acceleration similar to that caused by <span class="chemical">verapamil</span> ( n = 5 ) . 