In the juvenile (or tadpole) stage, the circulation is similar to that of a fish; the two-chambered heart pumps the blood through the gills where it is oxygenated, and is spread around the body and back to the heart in a single loop.
ɪnðə dʒˈuːvənˌaɪl ɔːɹ tˈædpoʊl stˈeɪdʒ, ðə sˌɜːkjʊlˈeɪʃən ɪz sˈɪmɪlɚ tə ðæt əvə fˈɪʃ; ðə tˈuːtʃˈeɪmbɚd hˈɑːɹt pˈʌmps ðə blˈʌd θɹuː ðə ɡˈɪlz wˌɛɹ ɪɾ ɪz ˈɑːksɪdʒˌɛneɪɾᵻd, ænd ɪz spɹˈɛd ɚɹˈaʊnd ðə bˈɑːdi ænd bˈæk tə ðə hˈɑːɹt ɪn ɐ sˈɪŋɡəl lˈuːp.