If you google the phrase “kidney transplant romance,” you'll find an entire page of books on Amazon.com devoted solely to kidney transplant romance novels. I am not even making this up. Similarly, if you google the phrase “heart transplant romance” you'll find the Amazon page for heart transplant romance novels, such as “A Valentine Heart” by M. Latron:
"George Valentine thought he could live forever on love alone. The day he died he gave his heart to another man who was in desperate need. Little did George know that he would be giving Ernest Harper more than just his heart, and that his wife Amy would finally find a way to heal."
I would never have imagined that romantic fantasies related to organ transplants could possibly be such a popular genre as to inspire an entire page of search results for each separate transplanted organ and its associated romantic entanglements, but there you have it. There is even a page of search results for sickle cell transplant romance novels. So, although I have not yet found a novel in which a man and a woman exchange a kidney and a heart and then somehow fall in love (wouldn't at least one of them be dead?) I am still pretty sure there's one out there somewhere.
Clearly, for reasons beyond my own ability to either quantify or understand, there is a certain type of romance fan that finds the whole notion of transplanted organs either breathtakingly romantic or disturbingly arousing or both. I know that a lot of romance novels are really thinly-veiled erotica, so I can only assume both factors are in play here. There's probably a whole section of the internet devoted solely to transplant erotica now that I think of it, but I just can't bring myself to google it and find out for sure.