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: Both isomers of propranolol were also capable of reversing ventricular tachycardia caused by ouabain in anaesthetized cats and dogs .
### Output Text:
Both isomers of <span class="chemical">propranolol</span> were also capable of reversing ventricular tachycardia caused by <span class="chemical">ouabain</span> in anaesthetized cats and dogs . 