Baretti: A dictionary of the English and Italian languages
Pétt-o, s. m. Pétt-óra, pl. f. aug. Pétt-áccio,
1. breast; 2. mind, heart. Sfogare il —, to ease one's mind;3. a man. Avere a — il bambino, to suckle a child. Uomo di —, a man of courage. Avere a —, to have a thing in one's heart. A —, in comparison of. Dar di — ad uno, to hit upon one, to meet him. Andare a —, to confront, face. Pigliare a —, to protect, defend. A — a —, face to face. Con forte —, boldly. Di tutto —, with all one's might. Metter a — di, to compare with. A — di voi egli non è ch'un bambino, he is but a baby to you.
Florio: a worlde of wordes, or most copious, dictionarie in Italian and English
petto: that part of a bodie beneath the channel or neck-bone, called the breast. Also vsed metaphorically for worth, valour, wit or bodily strength.