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: Significant increases in peak myocardial contrast enhancement and serological cardiac troponin I ( cTnI ) emerged after eight doses , importantly preceding the LVEF decline to < 50 % .
### Output Text:
Significant increases in peak myocardial contrast enhancement and serological cardiac troponin I ( cTnI ) emerged after eight doses , importantly preceding the LVEF decline to < 50 % . 