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: Epicardial coronary collateral vessels were demonstrated in all four patients ; a coronary " steal " phenomenon may be the mechanism of the dipyridamole - induced ischemia observed .
### Output Text:
Epicardial coronary collateral vessels were demonstrated in all four patients ; a coronary " steal " phenomenon may be the mechanism of the <span class="chemical">dipyridamole</span> - induced ischemia observed . 