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: On readmission , 11 patients received therapeutic heparin , which worsened the patients ' clinical condition and , in all 11 cases , decreased the platelet count ( mean at readmission , 143 x 10 ( 9 ) cells / L ; mean nadir after heparin re - exposure , 39 x 10 ( 9 ) cells / L ) .
### Output Text:
On readmission , 11 patients received therapeutic <span class="chemical">heparin</span> , which worsened the patients ' clinical condition and , in all 11 cases , decreased the platelet count ( mean at readmission , 143 x 10 ( 9 ) cells / L ; mean nadir after <span class="chemical">heparin</span> re - exposure , 39 x 10 ( 9 ) cells / L ) . 