be frank and forthright(/unreserved); be truthful in one’s words; carry(/wean) one’s heart upon one’s sleeve; say what one thinks; speak from the (/one’s)heart; speak the mind
❍ 就是我们……和几乎同类的人，只要什么地方有些不同，又得～，就往往免不了彼此无话可说。(《鲁迅选集》 Ⅳ—36) Even we…of ten find nothing to say to people who are more or less our own counterparts if we fail to see eye to eye yet have to speak from the heart.
心口如一xīn kǒu rú yī
心里想的和嘴上说的都一样。形容为人诚实、直爽。be honest and straight forward, say what one thinks, speak the minds, mean what one says, be frank and forthright