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: Heart rate ( HR ) , mean arterial pressure ( MBP ) , positive rate of increase of left ventricular pressure ( + LVdP / dt ) , echocardiographically assessed left ventricular ejection fraction ( LVEF ) , and fractional shortening ( FS ) , as well as chronotropic response to isoproterenol and exercise - induced sympathetic stimulation were evaluated under baseline and posttreatment conditions .
### Output Text:
Heart rate ( HR ) , mean arterial pressure ( MBP ) , positive rate of increase of left ventricular pressure ( + LVdP / dt ) , echocardiographically assessed left ventricular ejection fraction ( LVEF ) , and fractional shortening ( FS ) , as well as chronotropic response to <span class="chemical">isoproterenol</span> and exercise - induced sympathetic stimulation were evaluated under baseline and posttreatment conditions . 