The front of this card, I based on an image from the Season 7 episode "The Power of Three." Whovians should remember that Kate Stewart held a scanning device in front of the Doctor which showed that he did indeed have two hearts. What better to use as the cover of a Valentine, than a scanning device showing the Doctor's two hearts? They may be anatomically correct hearts inside a human body, but they're still hearts!
I found the image the hard way: I put the DVD in the computer, clicked on the episode, and went directly to the scene in question and paused it at just the right moment. I then took a picture of the heart scanner on my phone. The picture I will include here, however, was taken from Tardis Data Core:
Image of Kate Stewart's Scan from "The Power of Three" taken from Tardis Data Core
On the back of the card I wrote "Happy Valentine's Day" and based the letters on the Doctor Who font. In addition, I decorated the back of this card, with letters from the Gallifreyan alphabet. As a guide, I used this image of the Gallifreyan alphabet from Science Fiction and Fantasy Stack Exchange, a "a question and answer site for science fiction and fantasy enthusiasts."
Image of Gallifreyan Alphabet Copied from Science Fiction & Fantasy Stack Exchange
Well, I hope fans will get a kick out of it, and I'm hoping to do some more Doctor Who fan art in the future. I'd love to read any comments, criticisms, or suggestions for future projects. And of course, I'd love to see anything you've made as well.