A disappointing read. I'm honestly surprised that the author has written a NYT bestseller, because everything about this story felt clunky: heavy-handed exposition, stilted dialogue, and an abundance of telling rather than showing. The story tried far too hard to be quirky and cool, and ended up coming off as a poseur instead. I think the length worked against it, as well; doubling or perhaps tripling the length would've given the author a chance to be more subtle and leisurely in sketching out the universe for the reader.
"Heart Trouble" is like cotton candy; it's light and sweet and fluffy, but there isn't a lot of substance to it. That's not necessarily a bad thing—sometimes cotton candy is exactly what you want—as in the case of this well-written romantic fluff that's just long enough to satisfy.
Warning: If you're a medical professional, there are some dubious ethics involved that might make you twitch, so caveat lector.