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: Also the enhancement of verapamil effects on atrial beating was more pronounced at LNa than at LCa . ( ABSTRACT TRUNCATED AT 250 WORDS )
### Output Text:
Also the enhancement of <span class="chemical">verapamil</span> effects on atrial beating was more pronounced at LNa than at LCa . ( ABSTRACT TRUNCATED AT 250 WORDS ) 