3958
New beta - blocking drugs have been introduced which may prove beneficial in certain clinical situations since they exert more selective blockade of the cardiac receptors ( beta1 ) as opposed to smooth muscle receptors ( beta2 ) .
 cardiac receptors, beta1, smooth muscle receptors, beta2
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: GENE 
Text: {0} 
Answer:
 cardiac receptors, beta1, smooth muscle receptors, beta2