Answer:
Assonance
Step-by-step explanation:
'Assonance' is the figure of speech that has been employed in the given line from the poem 'Heart to Heart.' The repetition of identical vowel sound of 'u' with different consonants in 'just...clutch....muscle....mute' helps in creating the desired rhythm, make it catchy, and give it a smooth and flow-on effect. It also assists in emphasizing the message more impactfully that although her heart is a 'muscle' yet feel the feelings building up.