Or maybe they should call it the Hard Levels. I wasn't quite sure to include it as a Do or a Don't, considering that you basically get the same score for literally twice the amount of effort. To get to the Heart Levels, hit DOWN and START simultaneously at the opening screen. This combination adds 10 to each level (i.e. Level 4 becomes Level 14, and so on.)
Are they worth trying out? If you're a sadomasochist, yes. Then again, going through this sort of 'boot camp' training might better prepare your eye-hand coordination for the normal levels.