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: CONCLUSIONS : These findings demonstrate that ACE inhibitor therapy in most patients with CHF can be successfully titrated to and maintained at high doses , and that more aggressive use of these agents is warranted .
### Output Text:
CONCLUSIONS : These findings demonstrate that <span class="chemical">ACE inhibitor</span> therapy in most patients with CHF can be successfully titrated to and maintained at high doses , and that more aggressive use of these agents is warranted . 