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: When DSE is performed to evaluate coronary artery disease , not only fixed coronary stenosis , but also coronary spasm should be considered as a genesis of asynergy .
### Output Text:
When DSE is performed to evaluate coronary artery disease , not only fixed coronary stenosis , but also coronary spasm should be considered as a genesis of asynergy . 