4477
In the intact animal , postextrasystolic potentiation depended on the basic pacing interval , t0 , and the timing of the extrasystole , t1 : when t0 was held constant and t1 was increased , potentiation decreased ; when t1 was held constant and t0 was increased , potentiation increased .
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Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: GENE 
Text: {0} 
Answer:
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