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: We describe the cardiopulmonary resuscitation efforts on five patients who presented in acute circulatory failure from myocardial dysfunction .
### Output Text:
We describe the cardiopulmonary resuscitation efforts on five patients who presented in acute circulatory failure from myocardial dysfunction . 