This is all about layering your polish and your nail art.
You need to choose a polish that is a "jelly" meaning that it is rather sheer when you apply it. This will allow you to do the layering necessary to get the effect.
I started with one coat of a teal jelly from LA Colors Color Craze and then I drew in a few hearts (just 2 or 3). Then, once that is dry, you apply another layer of the polish and then draw on more hearts. Keep doing this until you've built 3 or 4 layers of hearts.
And just because I love me a good shimmer, I added on a topcoat of an LA Colors white shimmer.
There is an amazing tutorial for this over at Adventures in Acetone (one of the fabulous blogs that I follow), so check it out if you want to try this nail art.
Happy painting friends!