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: The cardiomyopathy is attributed 1 ) to the fact that radiation fields for left Wilms tumor include the lower portion of the heart and 2 ) to the interaction of doxorubicin and irradiation on cardiac muscle .
### Output Text:
The cardiomyopathy is attributed 1 ) to the fact that radiation fields for left Wilms tumor include the lower portion of the heart and 2 ) to the interaction of <span class="chemical">doxorubicin</span> and irradiation on cardiac muscle . 