。
Open up your heart and tell me everything.
Literal
True-heart [object-を] open-up-[sequential-て] everything [object-を] tell-[for-me-imperative-てくれ].
Two connected commands. 本心 ('true feelings, real heart') + 打ち明ける ('to open up, confide, reveal,' literally 'strike-open'). 話してくれ is the plain imperative of the benefactive 話してくれる — ~てくれ is a strong, urgent 'do X for me.' This stripped-down imperative form is characteristic of heated moments, male dialogue, or speakers with authority.