Heart and flowers modeled in Mathematica separately, then using MeshMixer to edit, scale and put them together.
This is also a part for my 3D printing project "Surprise Box".
Update A

The original file named "Flowery_Heart_Right_Size_2" is the basic concept of it, and although it looks nice, it is not printable on most of the 3D printers, because of several problems, like too many shells, the petals are too thin, etc.
The printable and updated version is named "ReallyFinally3stl_repariedsimplied". This one has been cleaned, made solid, checked errors, strengthened and simplified. Therefore, this one is more suitable for printing. I will test it within a few days and put on the picture of the printed version here later.
Also, since the original flowers were not suitable for printing, I changed the numbers of the formulas on Mathematica a little bit, and get some different shapes of flowers. (PS. If you notice, all the three flowers are different.) It is also interesting to discover that when I change the power of one of the formula, I will be able to generate something that looked like a butterfly! Therefore, I added the butterfly on the new version!
Use for Cleaning and simplifying: MeshLab, NetFabb Basic.
*Above software are all free.
Update B
Finally finished printing!
I used the powdery SLS material to print it, and the machine used with this material also gave me the hollow effect inside the heart.
:)
I know that SLA should work too! But SLA may be more expensive and compared with SLS, it is more fragile. However, SLA could give you a more smooth surface.