One of the coolest concepts I've seen thus far, but I found it nearly impossible to decipher what the beat was I was suppose to follow—especially when the wave begins and enemies begin marching.
Is it the music? The heartbeat animation? Something else? Anytime I felt like I was close to "on beat" the feedback noises from the heart threw me off.
Again, great concept. I think clearer markers of what rhythm is supposed to be followed would be a massive step up—keeping in consideration that other noises in the game impact the player's ability to carry out the objective.