In a moment of trust, he opened his heart to his friend about his fears.

opened 是动词 open 的过去式，open 本意是"打开"，这里用作比喻意义。 his 是代词 he 的所有格形式，表示"他的"。 heart 本义是"心脏"，在英语中常用来比喻"内心、情感"。 opened his heart 是一个固定表达，字面意思是"打开他的心"，实际表示"敞开心扉、倾诉心声"的意思。