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: RESULTS : Patients went home after hospitalizations that had included heparin exposure - - in most cases , with no thrombocytopenia recognized - - only to return to the hospital ( median , day 14 ) with thromboembolic complications .
### Output Text:
RESULTS : Patients went home after hospitalizations that had included <span class="chemical">heparin</span> exposure - - in most cases , with no thrombocytopenia recognized - - only to return to the hospital ( median , day 14 ) with thromboembolic complications . 