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: Prolonged elevation of plasma argatroban in a cardiac transplant patient with a suspected history of heparin - induced thrombocytopenia with thrombosis .
### Output Text:
Prolonged elevation of plasma <span class="chemical">argatroban</span> in a cardiac transplant patient with a suspected history of <span class="chemical">heparin</span> - induced thrombocytopenia with thrombosis . 