At this point, you may want to give your beating heart a place to live. A small box works well to contain the electronics and give a stable platform for the heart as it beats.
This one uses the Adafruit shipping box that came with the parts, but any base or box will do.
Place the power switch in the back, cutting two small holes for the cables to pass through.
Cut a thin opening where you'd like to place the potentiometer.
Screw the potentiometer into the box.
That's it, adjust the potentiometer to vary the beating frequency.