Looks and sounds very good!
Rather than spawning the blocks in the middle, have them come in from the side, so they don't spawn on each other.
Also, I don't think you should drop the score when they lose a heart. Might be better like this:
- Good move (Push 1 in gap / push A off screen) => Score + 1
- Bad move (Push A in gap / push 1 off screen) => Heart - 1