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: Knowing that heart mitochondria represent almost 40 % of heart muscle by weight , we conclude that the deteriorating effects of ADR on cardiovascular function involve mitochondrial structural and functional impairment .
### Output Text:
Knowing that heart mitochondria represent almost 40 % of heart muscle by weight , we conclude that the deteriorating effects of <span class="chemical">ADR</span> on cardiovascular function involve mitochondrial structural and functional impairment . 