The word 心爱 is formed by directly combining the concept of the "heart" (心) with the concept of "love" (爱). This is not a grammatical rule but a conceptual fusion, where the "heart" serves as the metaphorical source and seat of the emotion, intensifying and internalizing the feeling of "love" to mean something cherished deeply within one's innermost feelings. It creates a single, unified idea of affection that is heartfelt and personally treasured.