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: Antiarrhythmic effects of ( + ) - cibenzoline and ( - ) - cibenzoline were examined using two canine ventricular arrhythmia models .
### Output Text:
Antiarrhythmic effects of ( + ) - <span class="chemical">cibenzoline</span> and ( - ) - <span class="chemical">cibenzoline</span> were examined using two canine ventricular arrhythmia models . 