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: This shunt of blood via a patent foramen ovale occurred in the presence of a normal pulmonary artery pressure , and was probably precipitated by a propafenone overdose .
### Output Text:
This shunt of blood via a patent foramen ovale occurred in the presence of a normal pulmonary artery pressure , and was probably precipitated by a <span class="chemical">propafenone</span> overdose . 