Here is a knitted heart with smooth edges all around - thanks to short rows that allow you to shape the heart between cast-on and bound-off edges.
Instructions include Solid Heart, Broken Heart (or shall we say Shared Heart) and Two Color Heart.

Material:
Use a small amount of leftover yarn, whatever weight you have on hand.

Dimensions:
Worked with worsted yarn on size 6 needles, the solid heart measures about 2 1/4 inches square; worked with bulky yarn held double on size 15 needles, it measures about 4 1/3 inches square.