The mammalian heart has four chambers, and oxygenated and deoxygenated blood are kept entirely separate.
ðə mæmˈeɪliən hˈɑːɹt hɐz fˈoːɹ tʃˈeɪmbɚz, ænd ˈɑːksɪdʒˌɛneɪɾᵻd ænd diːˈɑːksɪdʒˌɛneɪɾᵻd blˈʌd ɑːɹ kˈɛpt ɛntˈaɪɚli sˈɛpɹət.