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: A 79 - year - old woman presented with typical ischemic chest pain , elevated cardiac enzymes with significant ST - segment abnormalities on her electrocardiogram .
### Output Text:
A 79 - year - old woman presented with typical ischemic chest pain , elevated cardiac enzymes with significant ST - segment abnormalities on her electrocardiogram . 