Looking for a unique, romantic symbol of your love? Look no further than a heart-shaped diamond ring! A 3-carat heart-shaped diamond will measure about 9.46mmx9.46mm. However, the size of a heart-shaped diamond will vary depending on its cut quality and its length-to-width ratio. Not sure how to wear your heart-shaped ring? Typically, a heart-shaped diamond ring is worn with the point facing you.