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: The bradycardia lasted ~ 2 h , and further cardiac workup revealed no underlying abnormality .
### Output Text:
The bradycardia lasted ~ 2 h , and further cardiac workup revealed no underlying abnormality . 