xīn heart (left-side form)

Forms

• 心 bottom — Full form, written at the bottom of a character.
• 忄 left — Compressed upright form, written on the left.

Characters that use it as a component

忆忙忧快忱怀怔怕

Characters filed under it as a radical

Kangxi radical no.61 · 心 · 4strokes — The 214 Kangxi radicals

Filed under it in a dictionary. That is a lookup convention — it does not mean it is the only part the character is built from.

心必忆忌忍志忘忙