忄

Three strokes on the left of a character — that's the inner-life signal. 忄 marks emotion, mood, and mental state in characters where the phonetic sits to the right. The shape is the heart radical 心 stood on its side and slimmed for a side-by-side compound; it's never written on its own.

忄 is the calligraphic compression of 心. When 心 needs to share a square with another component to the right, scribes rotate the four-stroke heart into a tight vertical column: a downstroke flanked by two short ticks. The radical's identity as 'heart' is preserved, but the silhouette is unmistakably side-positional.

Strong feeling/mind cue: 忙 (busy), 怕 (afraid), 快 (fast/happy), 慢 (slow), 情 (feeling), 怀 (cherish), 性 (nature/disposition).