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: During dipyridamole - induced hyperemia , 12 of the 16 dogs with a partial coronary stenosis had a visible area of hypoperfusion by contrast echocardiography .
### Output Text:
During <span class="chemical">dipyridamole</span> - induced hyperemia , 12 of the 16 dogs with a partial coronary stenosis had a visible area of hypoperfusion by contrast echocardiography . 