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: Acute heart failure was induced by propranolol and volume loading after weaning from cardiopulmonary bypass ; an absence of MR was confirmed by echocardiography .
### Output Text:
Acute heart failure was induced by <span class="chemical">propranolol</span> and volume loading after weaning from cardiopulmonary bypass ; an absence of MR was confirmed by echocardiography . 