Annie’s struggle to understand the changes in her world is a story of discovering and embracing the rhythms of life. The rhythmic refrain of “thump-thump, thump-thump,” present throughout Heartbeat, is introduced as the sound of Annie’s feet running in the first poem of the book. It is also the sound of a heartbeat itself, which becomes an important symbol of life for Annie when she hears her unborn brother’s heart (75). Annie’s relationship with her friend, Max, is defined mainly by their shared love of running, and the “thump-thump” of their feet also becomes a rhythm of conversation and communication (184).

Other rhythmic refrains are present throughout the poems that comprise the story. The pages of Grandpa’s photo album go “flip, flip, flip,” and with the pages, his life moves forward (85). The cycle of breathing in and out is often repeated by Annie as she describes her runs (29). However, as Annie’s mother struggles to deliver her baby, “breathe in, breathe out” is repeated as an instruction by Annie’s father. The refrain then changes meaning in Annie’s narration as well, as she contemplates the cycle of childbirth and motherhood: “I think of all the mothers / all over the world / and all the babies / and I was one of those babies / and this is my mother / and maybe this will be me one day / breathing in, breathing out” (155).