I have already posted tutorials about Making Shadow in Photoshop and Making 3D TV on Photoshop, so now i am posting a tutorial on making a 3D heart. You can send it to your loved one :P
Our final image can be like this...

Lets put a gradient of your desired color, as we always do :P
Now create a heart from custom shape tools
Then apply the settings shown below in your Blending Options and press okay. (to open blending option double click on the layer.)
Then create a new layer by pressing "Shift+Ctrl+N"
Then select the round edges of the heart by Elliptical Marquee Tool, (we will use it to show little glow). Then put white gradient in it as shown below
Now decrease the opacity of the new created layer and remove the half rounded circle as shown below...
Now go to layer and right click on it, click on duplicate layer. You will get a duplicated layer of the heart now
Then "Free Transform" and rotate the heart to 180 degree.
After rotating the heart decrease its size as shown below, (we want to make it look like shadow on earth)
now Decrease the Opacity of the Duplicated Layer and remove it little bit as shown below
Your heart is ready but you want to give it a more nice look then click on "Custom Shape Tool" and select "Registration Target 2" shape.
Draw the custom shape as below
Then Drag the Heart Layer on the top of the custom shape as shown below...
Now decrease the opacity of the Custom shape and you will get the image s shown below... :)
Now your Heart, i mean 3D heart is ready. Create your own if you want to give it to any one. But please tell me that who is the lucky person... :D