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: These effects gave rise to an increase in the right atrial pressure and a decrease in the left one with a consequent stretching of the foramen ovale and the creation of massive right - to - left shunting .
### Output Text:
These effects gave rise to an increase in the right atrial pressure and a decrease in the left one with a consequent stretching of the foramen ovale and the creation of massive right - to - left shunting . 