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: Even if it did not reach statistical significance because of a few number of cases , the risk was lower in trials excluding patients with cardiac history , and seemed to be higher in trials including patients with pre - existing cardiac diseases .
### Output Text:
Even if it did not reach statistical significance because of a few number of cases , the risk was lower in trials excluding patients with cardiac history , and seemed to be higher in trials including patients with pre - existing cardiac diseases . 