Meaning of nèi xīn:
nèi xīn
内心
Noun
heart; innermost being; (math.) incenter
Tā de biǎoqíng píngjìng, dàn tā de nèixīn què zài xiōngyǒng-pèngpài.
她的表情平静,但她的内心却在汹涌澎湃。
Her expression was calm, but her heart was turbulent.
Měi gè rén de nèi xīn dōu yǒu yī gè mìmì.
每个人的内心都有一个秘密。
Everyone has a secret in their heart.