Both are "Slice of Life" shows, that are slow paced, have very little plot, a bit of drama (and very small hints at romance), both involve a group of friends and their relationship with the lead character (Piano Main Character: Miu Nomura ||| To Heart Main Character: Hiroyuki Fujita). Both shows lack action, and have a very limited use of humur. Both shows have a bunch of interesting characters (that don't do anything interesting the entire series), and both shows can be considered "coming of age stories". Also both To Heart and Piano are realistic (well To Heart has some non-realsitic parts). However both shows are different takes on this genre. To Heart follows a male lead, while Piano follows the female lead. If you like To Heart, watch Piano! If you like Piano watch To Heart!