胸がいっぱい (overcome with emotion)

The body-part idiom 胸がいっぱい (often 胸がいっぱいになる, 'one's chest becomes full'), literally 'chest is full,' meaning 'heart is full, overcome with emotion, overwhelmed.' Used for grief, joy, gratitude, bittersweet feeling — any emotion strong enough to fill one up. 胸 ('chest') plays the metaphorical role English gives to 'heart.'