This is a really simple heart design that can be done with a nail brush. Before actually trying anything on your nails I would suggest that you test it out on paper or a friend first.
The heart design is composed of two simple brush or pen strokes. All that is needed is two lines intersecting together at the bottom point of the heart. They will look like this:
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Pictured on this post is Sally Hansen's Xtreme wear in Turquoise.