Looking for advice

Hi I am looking for a way to control a motor of some sort and make it imitate a heart beat I do costume for renaissance fairs and I want to have a fake heart on my costume and I want it to turn gears to imitate a mechanical heart beat and I want it on a dial to increase speed

I would use a hobby servo to drive two small bellows in a heartbeat pattern. See File->Examples->Servo->Sweep for an example of running a servo at a slower-than-maximum speed.