。
Without a word, our hearts connected.
Literal
Be-silent-[and-て] heart [subject-が] passed-through.
心が通う ('hearts pass through to each other') is a beautiful set phrase for a wordless mutual understanding — souls in tune, no need for speech. Note the verb 通う ('to commute, pass through, frequent') used with hearts as the subject: a metaphor of one heart's signal travelling through to the other. The te-form 黙って turns 'being silent' into the manner of the connection.