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: However , dP / dt in the ISO - treated hearts was slightly but significantly ( P less than 0 . 05 ) elevated .
### Output Text:
However , dP / dt in the <span class="chemical">ISO</span> - treated hearts was slightly but significantly ( P less than 0 . 05 ) elevated . 