Fig.: to speak in all sincerity. To show one's feelings openly

Susan is very honest and sincere: she cannot hide her feelings and she always wears her heart on her sleeve

Susanna è una persona molto onesta e sincera: non riesce a nascondere i suoi sentimenti e parla sempre a cuore aperto

"You look like you don't care of what's happening to our family" "I care alright, it's just that I don't wear my heart on my sleeve"

"Sembra che non ti importi niente di quello che sta accadendo alla nostra famiglia" "Mi importa invece, è solo che non lo do a vedere"

I'm in a bad mood; maybe I'll feel better if I open my heart to you and wear my heart on my sleeve

Sto passando un brutto momento; vorrei confidarmi con te e parlarti col cuore in mano: forse dopo mi sentirò meglio

It was once a custom for a knight to pin a gift from the lady he loved to his sleeve before going into combat, thus displaying his feelings. It was Shakespeare's Iago, who wore a heart on his sleeve, thus professing a devotion to his master Othello. In Othello (1:1) Iago says:
For when my outward action doth demonstrate
The native act and figure of my heart
In compliment extern, 'tis not long after
But I will wear my heart upon my sleeve