inner heart; depths of one's heart
Refers to the deepest, most private part of one's feelings or thoughts. Often used in emotional or introspective contexts.
Deep in her heart, she still loved him.
I revealed a secret I had kept hidden in the depths of my heart.
Compound of 心 (heart, mind) + の (possessive particle) + 奥 (inner part, depths). The phrase is transparent and follows standard Japanese compounding.