This pastime of medical pareidolia peaks at certain times of the year, particularly on February 14th and April 1st. A number of examples of this have been published in the American Journal of Roentgenology, not only one of the most respected peer-reviewed radiology journals in the world, but also one of the few with a sense of humor.
A search of the AJR archives and other radiology sites brought up a number of hits for "Valentine". If your sweetie has adventuresome tastes and you still haven't found just the right card, click through the following links for some ideas. There you will find a variety of "hearts" discovered in the midst of other organs, such as a pulmonary bulla, the bladder, Zeus only knows (some part of the gut, I think), the bladder again, the prostate, a cerebral aneurysm, the spine, the stomach, another aneurysm, a Fallopian tube, the spleen, a barium enema of the colon and other sites. One final canonical article on this topic contains no less than 27 examples of other ectopic "hearts" found by its authors.
If your taste turns to somewhat less anatomically explicit valentines, Ironic Sans has some other ideas for your scientific squeeze:
I’ve decided to honor an entirely different group of people with this collection of romantic cards you can e-mail to your loved ones on February 14th, or any other day of the year. It’s Scientist Valentines!♥ tip for this last quote to Bad Astronomy