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: This is the first patient to initially manifest tricuspid regurgitation and atrial flutter , and the 11th described patient with cardiac disease among infants exposed to lithium compounds in the first trimester of pregnancy .
### Output Text:
This is the first patient to initially manifest tricuspid regurgitation and atrial flutter , and the 11th described patient with cardiac disease among infants exposed to <span class="chemical">lithium</span> compounds in the first trimester of pregnancy . 