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: Isoproterenol alone decreased left ventricular systolic pressure and myocardial contractility indexed as LVdp / dtmax and LVdp / dtmin .
### Output Text:
<span class="chemical">Isoproterenol</span> alone decreased left ventricular systolic pressure and myocardial contractility indexed as LVdp / dtmax and LVdp / dtmin . 