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: A case is presented of a reversible intra - Hisian block occurring under amiodarone treatment for atrial tachycardia in a patient without clear intraventricular conduction abnormalities .
### Output Text:
A case is presented of a reversible intra - Hisian block occurring under <span class="chemical">amiodarone</span> treatment for atrial tachycardia in a patient without clear intraventricular conduction abnormalities . 