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 : In patients with mechanical heart valves , short - term LMWH therapy compares favorably with UH .
### Output Text:
CONCLUSIONS : In patients with mechanical heart valves , short - term <span class="chemical">LMWH</span> therapy compares favorably with <span class="chemical">UH</span> . 