A clockwork heart sculpture. As the left side spins continuously, the piston drives the right side intermittently.
The instructions have it manually powered using a hand crank in the back, but it can easily be motorized by attaching an M-Motor to the back. I illustrate one way of doing this towards the end of the video.
The relatively new long Technic axle pin (the only black part in the instructions) can also be replaced by a regular axle if you want. The axle pin just results in a little smoother motion.
For the part list I'm using the most common colours of most of the gears, but they all come in light gray if you want to make look uniform.