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: Treatment with a PJ34 significantly improved cardiac dysfunction and increased the survival of the animals .
### Output Text:
Treatment with a <span class="chemical">PJ34</span> significantly improved cardiac dysfunction and increased the survival of the animals . 