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: All 7 patients ( 13 . 7 % ) had chest pain during asynergy , and both chest pain and electrocardiographic changes were preceded by asynergy .
### Output Text:
All 7 patients ( 13 . 7 % ) had chest pain during asynergy , and both chest pain and electrocardiographic changes were preceded by asynergy . 