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: We conclude that in patients with chronic coronary artery disease who are not in clinical congestive heart failure left ventricular end - diastolic volume falls after ouabain administration even when it is initially normal .
### Output Text:
We conclude that in patients with chronic coronary artery disease who are not in clinical congestive heart failure left ventricular end - diastolic volume falls after <span class="chemical">ouabain</span> administration even when it is initially normal . 